Do men masturbate in condoms?

My husband and I used a condom once when we dated, so he had some leftover as our relationship progressed. I'm not too proud of myself to say that I snooped to check how many were left and noticed one day when he was at work that one was missing. I had his phone password, a key to his house, and really no reason to believe he would do anything to disrespect me on this level. Any paranoia I've ever had with him turned out to be strictly paranoia from previous relationships, manipulation, and cheating... unrelated to him.

When I confronted him, he was obviously uncomfortable that I snooped, saying "I didn't know you were counting them. It's embarrassing, but I used it to masturbate. It's cleaner."

I've operated on giving him the benefit of the doubt since and still have never found any evidence of cheating. He has lied about some stupid stuff, like saying he doesn't watch porn, when he does (and he knows it doesn't bother me). I can see him not wanting to waste the condoms if we weren't going to be using them, but I don't want to be naive.

When I've searched online, most people say it's an excuse, but somewhere in the threads, people will say that although it's not common, some men do this. Really curious for a man's perspective.