My ex used to fake a deeper voice every time he met this particular friend and it still confuses me

He's 34 and I'm 30.

So, for some reason that's embarrassing. We broke up a month ago after four years together, and I just wasn't able to ask him about it.

During the time we were together, every time he met this particular friend of his, when he was back home he talked with a fake deeper voice. It was not as a joke or something like that, it was him pretending it was his normal voice.

When I asked what was wrong with his voice, he seemed a bit nervous and just said something like "I have a sore throat" or "I must have caught a cold". Then next day or even after hours, his voice was back to normal.

It felt so weird but since he's really sensitive and I didn't wanna hurt his feelings, I never asked directly about it.

What could be the reason of this? Has anyone ever seen someone behaving like this?