[Shado-Pan Geyser Gun] is listed as a boss in throne of thunder.

According to wowhead:
https://www.wowhead.com/item=98132/shado-pan-geyser-gun
It's a toy reward from the achivement "Tortos Hidden Geyser Achievement"

It's not listed as a boss. It's listed in between the two bosses so you know where exactly in the raid order you need to do the achievement. Linking it under a boss would make it look like the boss' themselves drop it.

Yeah, it's listed logically in the raid where you would encounter it. This is working as intended.