I’ve seen people use this part to discredit the Trans Lars headcanon but I think they’re just looking for stuff to discredit it. There’s so much more that you can read from this if Lars is trans.
I think it’s possible Steven knows about Lars, that at some point in the past Lars told Steven, opened up to him. Steven’s carefree attitude towards Lars, seeing him as his friend and trusting that he likes him regardless of how much Lars seems distant or condescending to Steven, is because Lars already been open with Steven, and Steven knows that Lars’ distancing is a facade.
This is why Steven sees it as funny touching Lars’ chest (where his breasts or binder would be), he’s Lars confidant, and Lars’ is not embarrassed or shocked by Steven making a low-key joke than he is annoyed.
I think this narrative fits their relationship in proceeding episodes much better than ‘Lars isn’t trans, he’s just a dick to Steven’