AITH for telling my wife I’m uncomfortable with her going skinny dipping

Recently my wife (44f) went to a concert with a single female friend and my brother in law (wife’s sister’s significant other). After the show they met two guys and hung out. The single friend and the two guys ended up going skinny dipping while my wife and BIL did not.

Now my wife and I are having a disagreement about the situation. She believes it would have been fine for her to participate while I disagree. She believes I’m being controlling. AITH?