I'm fairly sure that SoundHound does not match hummed or sung queries with album recordings, but with other hummed melodies submitted by users and labeled with

I'm fairly sure that SoundHound does not match hummed or sung queries with album recordings, but with other hummed melodies submitted by users and labeled with the song ID. I would imagine the algorithm is different, since the Shazam algorithm is designed to find exact matches corrupted by noise, EQ, etc., and two hummed versions of the same melody may vary in key, tempo, and timbre, and have small rhythmic differences.