Music loops are being categorized as instrument samples. I'm contacting uploaders to help clarify and hoping the documentation will be updated soon.
You currently have to go to the description or sound edit page to see the parent category definitions so I'm putting the full table here while it's missing from the FAQ:

For searchability:
- Music (m)
- Description: Music excerpts, including melodies, singing, loops, fillers, drones and short musical snippets.
- Music / Solo percussion (m-sp)
- Description: Music excerpts with solo percussive instruments.
- Examples: rhythmic patterns, un-pitched percussion excerpts
- Music / Solo instrument (m-si)
- Description: Music excerpts with only one instrument, excluding percussion.
- Examples: isolated melody or sequence of notes, solo singing, chords from one instrument
- Music / Multiple instruments (m-m)
- Description: Music excerpts with more than one instrument.
- Examples: orchestra, band, dueto, multi-instrument composition
- Music / Other (m-other)
- Description: Music that doesn't belong to any of the above categories.
- Instrument samples (is)
- Description: Single notes from musical instruments, various versions of the same note, and scales.
- Instrument samples / Percussion (is-p)
- Description: Instrument samples that are percussive (idiophones or membraphones).
- Examples: drum, snare, gong, bell
- Instrument samples / String (is-s)
- Description: Instrument samples that belong to the string instrument family.
- Examples: guitar, violin, harp
- Instrument samples / Wind (is-w)
- Description: Instrument samples that belong to the wind instrument family (aerophones).
- Examples: woodwind, brass, flute, trumpet, saxophone
- Instrument samples / Piano / Keyboard instruments (is-k)
- Description: Instrument samples of piano or other keyboard instruments, not synthesized.
- Examples: piano, organ, accordion, xylophone
- Instrument samples / Synths / Electronic (is-e)
- Description: Instrument samples synthesized or produced by electronic means.
- Examples: synthesizers (analog/digital), electronic samples
- Instrument samples / Other (is-other)
- Description: Instrument samples that don't belong to any of the above categories.
- Speech (sp)
- Description: Sounds where human voice is prominent.
- Speech / Solo speech (sp-s)
- Description: Recording of a single voice speaking, excluding singing.
- Examples: talking, script reading
- Speech / Conversation / Crowd (sp-c)
- Description: Several people talking, having a conversation or dialogue.
- Examples: playground, people talking in public places, conversations
- Speech / Processed / Synthetic (sp-p)
- Description: Voice(s) from an indirect source (e.g. radio), processed or synthesized.
- Examples: phone/radio recordings, robotic voice, text-to-speech
- Speech / Other (sp-other)
- Description: Voice-predominant recordings that don't belong to any of the above categories.
- Sound effects (fx)
- Description: Isolated sound effects or sound events, each happening one at a time.
- Sound effects / Objects / House appliances (fx-o)
- Description: Everyday objects, inside the home or smaller in size.
- Examples: daily or small objects, tools, weapons, clothes, iron
- Sound effects / Vehicles (fx-v)
- Description: Sounds produced from a vehicle.
- Examples: car passing by, car screeching, wiper, car brake, bike, plane, ship
- Sound effects / Other mechanisms, engines, machines (fx-m)
- Description: Machine-like sounds, except vehicles and small house electric devices.
- Examples: gear, clock, drill, lawn mower
- Sound effects / Human sounds and actions (fx-h)
- Description: Sounds from the human body, excluding speech.
- Examples: breath, heartbeat, sneeze, walking, jumping, hands, clap
- Sound effects / Animals (fx-a)
- Description: Animal vocalizations or sounds.
- Examples: cat, insect, sheep, animal walk, growl, purr
- Sound effects / Natural elements and explosions (fx-n)
- Description: Sound events occurring by natural processes.
- Examples: wind, fire, ice, rocks, water, stones, explosions
- Sound effects / Experimental (fx-ex)
- Description: Experimental sounds or heavily processed audio recordings.
- Examples: reversed sounds, weird effects, unusual recording techniques or processing
- Sound effects / Electronic / Design (fx-el)
- Description: Sound effects that are computer-made or designed for user interfaces or animations.
- Examples: sci-fi, laser
- Sound effects / Other (fx-other)
- Description: Sound effects that don't belong to any of the above categories.
- Soundscapes (ss)
- Description: Ambiances, field-recordings with multiple events and sound environments.
- Soundscapes / Nature (ss-n)
- Description: Soundscapes from natural habitats.
- Examples: forest, sea, river
- Soundscapes / Indoors (ss-i)
- Description: Soundscapes from closed or indoor spaces.
- Examples: closed room ambience, room tone, office, factory, bar
- Soundscapes / Urban (ss-u)
- Description: Soundscapes from cityscapes or outdoor places with human intervention.
- Examples: city ambience, outside airport, busy road
- Soundscapes / Synthetic / Artificial (ss-s)
- Description: Soundscapes that are synthesized or computer-made ambiences.
- Examples: artificially-created soundscapes, soundscapes from imaginary places
- Soundscapes / Other (ss-other)
- Description: Soundscapes that don't belong to any of the above categories.
Feel free to share if you notice other categorization mistakes or if you have thoughts on how to steer the UI/UX towards correct categorization