A smell is also a form of benefit that is forbidden from leavened food.
The question definitely seems like a serious question.

The smell of cookies is not cookies. Are there cookies inside the shampoo? It seems like trolling to me, or “a ridiculous joke,” as he would say.

Does the Rabbi think there is room to be stringent about these things on the grounds that it isn’t appropriate?
Suppose you take mouthwash with the flavor of actual leavened food, and everyone thinks you ate biblically forbidden sourdough bread. Is that a problem?

If people think he is eating leavened food, there is an issue of appearances. But I don’t think that is really the situation. Certainly if we’re talking about a person who observes Jewish law and there is no suspicion that he ate leavened food, then people wouldn’t think that.