Why did he react this way when I guessed he had a child?

So this guy and I used to date briefly over a year ago. Then he got into a serious relationship.
Fast forward to this day. We got back in touch a few months ago. He wanted to show me his new house so I came. He told me right before we met that he was in a relationship and actually moving in with her because I asked him if the house was for him alone.
Nevertheless, he was very touchy feely with me when I was there. He kept mentioning what had happened between us and said how he thought about it sometimes. He tried to initiate but I stopped him.
After that he was very flirty and making sexual innuendos by message or the phone. He tried to convince me to just let myself go and enjoy.
But recently based on some picture he shared I guessed he was having a child. I asked him and he simply replied “yes”. I congratulated him and he did not reply. I tried calling him and although he would say he’d call back he didn’t.
i can not understand this reaction.
why is he acting this way?
He did not mind letting me know he was ready to cheat on his girlfriend whom he has been making serious plans with. Why me knowing that he’s having a child makes it any different?
Do you think it’s Shame? Or he thinks that he can’t get anything from me Now that I know his whole situation so he just let it go?
what do you think is the reason for his silence?
i don’t get it.
Why did he react this way when I guessed he had a child?
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