AITA for grounding my 14-year-old son for going skinny dipping?

I (35F) went to visit my friend (37F) last week and I took my son (14M) with me. My friend has a swimming pool and my son brought his swim trunks with him in case he decided to swim. My friend has two daughters (13F) and (14F). My son and my friend's daughters said they were going to swim in the pool but when me and my friend looked out the window we saw the three of them completely naked in the pool. I grounded my son and forbade him from using his phone and Nintendo Switch. My husband thinks I overreacted. AITA?