I get what they're saying about it being out-of-tune. The synth melody is in the key of B-flat major but the item pick-up sound/error sound's melody is in the key of D major.
Also, "sub-melodies" isn't the correct term; it's "counterpoint" or polyphony. The synth does the main melody while the item pick-up sound does a counterpoint melody.
Very experimental. I'll give it that. Hard to make sound effects into a good song, so I admire the attempt. Kinda sounds like something you'd hear in a demented fun house, honestly.
You see what I'm trying to do here people? This is known as "constructive criticism." Don't just complain about the song being bad, tell him how it can be improved.