I think that just refers to 50 different items altogether… like, you have 50 “inventory slots”, as it were, so items like smileprin that stack count as 1 item.

There was a thread a while back where someone tried to collect one of every junk and ran into that barrier, which is what makes me think it’s the slots theory, because otherwise he surely would’ve run out of room before he could get his 50th junk piece because of his consumables.