It's fine warning about a spoiler from a specific source. But don't go extending that to open spoilers or confirming the original post. If I go in the GoT spoiler thread, tell everyone how Endgame ends and then say "Spoilers dude, in the title!" what would happen? The Spoilers refers to the Jack in the Box advert and nothing else. It is not fair to treat this as an open spoilers thread.
I couldn't give a fuck about spoilers personally, I've read all of them, but this advert is probably just guess work and yet people have used it to piggyback spoilers into a thread that is purely about spoilers in the advert. Do you not think that people will have seen the advert already and want to discuss whether it may be true without getting confirmation?