My boyfriend brought up how upset he was about something dealing with his ex-girlfriend..HELP?

Me and my boyfriend of 3 weeks were walking and talking, and he brought up this one festival (that was like a month and a half ago) that he went to that was in our town and he said that he was very angry that day, and was angry about it for days and he had to vent to his friend Andrew about it for hours. I asked him why he was mad and he said that it was something his friend John said about someone. Right as he said that I knew what he was talking about, although he didn't know that I know. I know from another friend that he was angry that day because his friend John said something really disrespectful about his then-girlfriend, who is also one of my good friend's. So, I pretended to not know what it was that John said that made him angry that day and I'm just like "Tell meeee" and all that and he's all like "No no, I mean I'll tell you one day.." And I'm just teasing him sorta like "Come onnn. Will you ever tell me?" And he's like "Probably not!" And I'm like "Well, why can't you tell me?" and he's like "Because, I don't think it's something you would feel comfortable discussing." And with that it ended. Ugh, do you think he's still into his ex because he brought it up and was very upset about it back then, and still kind of annoyed that his friend John would say that? Or am I just reading into it too much? thank you!