The man I am exclusive with talked a woman for hours at a bar, but was honest-should I be concerned?

I was supposed to get a phone call the evening that my boyfriend decided to go out on his own. He ended up at a bar (he is generally very friendly and talks to everyone) whereby he sat and talked with a woman for a few hours. At first he emailed me to let me know he was out and that he met "someone" very interesting. He attempted to negate gender from the email. Once I spoke to him, however, he mentioned that 'she' was x,y,z and talked about different things. I communicated that I wasn't thrilled about this, being that he was supposed to give me a call and neglected to do so, instead drinking/chatting with someone for hours. He then told me I had no reason to be jealous, and that he'd never cheat on me and would always be honest with me, just as he was then. I trust him, however I do have some concern- While this situation didn't lend itself to cheating, who knows what else could come down the line? This woman was apparently much older than he (in her 40's) and that even though she gave him her number, "I should not be jealous" as it was a friendly thing. He also mentioned that he gets numbers once in a while from girls when he is out with his friends, but throws them away. Am I nuts, or wouldn't this entail talking to these girls for a while before they produce a phone number? Sighhhh. I do believe I am dealing with someone who is a bit immature, right? Thanks for your input-I look forward to reading your response(s)