Even if that's true, this bug still occurs in Gen 6 and possibly previous gens too. Here's an example from only a couple of pages back:To my knowledge, as of gen 7 you need to have an item to use trick. This was not the case in gen 6, so if those sources haven't updated since then that's probably why.
http://replay.pokemonshowdown.com/pu-513830822
turn 34, i clicked trick with my itemless mr. mime against a metang holding an item. the move failed. earlier in the game, i had tricked my choice scarf onto a clefairy, also holding an eviolite, which proceeded to knock off the eviolite my mr. mime stole. in-game, trick only fails if neither pokemon is holding an item, and it doesn't matter if the items are the same.
ive noticed this happen several times recently, but this is the first time it happened during one of my games. it seems to be a recent bug, ive been able to trick items purely away before.
this game is gen 6 pu. i don't know if something in sun and moon changed trick's mechanics, but if it did, its affecting gen 6. according to bulbapedia, trick's mechanics were not changed, but its bulbapedia.
I have no idea whether the mechanics were changed in Gen 7 and I'm not able to test it, but either way this is still a bug in Gen 6 (assuming my sources are correct).