jounniy
Thats funny, because I’ve seen some DMs where nobody cares wether or not lvl. 10, they still treat you as if you were lvl. one and don’t know sh*t about you. (Mainly in campaigns where the characters travel a lot. I still find it weird. Rumors spread quickly.)
Far as I think about it, if one wants to hide a spell, they should pick up the subtle spell-metamagic. Making every caster able to do what is supposed to be a special ability (on par with doubling the range/duration of a spell) cheapens the ability and makes casters even stronger than they already are.
If he doesn’t know what spell you’re casting, that means that he’s even more likely to assume that you are trying to cast an harmful spell, making him attack you. And casting a spell takes an action, basically a third of your turn if you want, so the hobgoblin has at least 2 seconds to react, if not more. And thats plenty of time to stop himself from jumping.
Casting a spell and holding it uses visible components the hobgoblin could react to.
Incite greed also explicitly says that the creature avoids obvious harm while approaching you and does nothing beyond approaching you. If the would always run after the gem (forsaking personal safety to do so), this would be noted in the description.
I assumed it to be about weird interpretations/effects of spell that are either Raw but stupid (like find traps finding intentional clauses in legal documents) or common sense interpretations that still lead to weird outcomes (using bead of force+levitate+thunderwave to blast the BBEG into orbit). Because why make a video about people misinterpreting spells without making clear that this is unintended?