Why would a guy who wouldn’t commit be upset that I now have a boyfriend?

I dated this guy earlier this year and he said that he couldn’t commit because he was too busy to be in a relationship and wasn’t over his ex. I started distancing myself from him when I met my boyfriend and fast forward to now, I take a picture with my boyfriend and posted as a story on IG. Then lo and behold, I get a message from Mr. Non-Committal and he asks if he’s (my boyfriend) the reason why he and I fell out.

While I have zero interest in this man now, I wonder why he has all these questions now?
Why would a guy who wouldn’t commit be upset that I now have a boyfriend?
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