Talking to ex and bf mad

So my ex and I had 4 years together and we ended on good terms. It’s been almost a year since our breakup and haven’t talked much. Today he was passing by my house and he stopped by to say hello and what’s up we catched up for 2 mins or less and that’s it. I told my boyfriend about our talk and how long we talked for and he still got upset saying he is disappointed and that we need to talk. How can I make him understand that it’s nothing? We’re all mature and adults and I feel like this shouldnt be a problem. Help