By legitimate reason I don't mean you specifically, but like the workplace vibe in general or a specific past experience. You should absolutely have a talk about it, there might be more important things to address than the choice of emoji.

As for that other possible cause - I have friends who frequently discuss degenerate online-brained behaviors they witnessed and I found myself later second-guessing interactions I had online as a result. It took me a while to realize my brain was slowly getting poisoned by this discourse.