I would say that the string "Melbourne Bounce" contains (has) the string "bounce" - so everything is fine.
The shorter the string and the further it is from being unique, the more matches you get.
This is a substring filter, showing every file that has Kick+Clap/Snare in one of the genre fields. This means that it can also contain more text around the search string, e.g., Kick+Clap/Snare + ? which has an extra + ?
If you want an exact match, use genre IS "Kick+Clap/Snare"