Did he lie?

Back in May, I met someone who I have developed strong feelings for. We've had sex, and every single time we have, he has been paranoid about getting me pregnant. I explained the first time that I have an IUD and am not worried about accidental pregnancy. I've honestly never been with a man who is this nervous about it. 
Well, then one day during a conversation, he tells me he had a vasectomy many years ago. Um, ok? So you're worried about getting me pregnant why? Yes, it does happen, but VERY rarely. It's a 1 in 4000 chance! Not to mention, vasectomy + IUD seems like a sure fire way NOT to get pregnant. 
Last week, he came over and we had sex. During the sex, he began to talk about how he doesn't want to get me pregnant. I said "I have an IUD, and you're fixed, I don't get it." He looked away, avoided the vasectomy thing and repeated "we CANT have a baby" and then said "I really hope your IUD works." At that point, he finished inside me. 
I have this nagging gut feeling that he lied about being snipped. But what I don't understand is why? Why would a man lie about that? It's been bugging me, so I thought I'd ask for some opinions. 
***Everyone, he's not married, I promise. We met through work/close friends. He's divorced and has one child. He and his ex didn't want any more kids together because she's never home due to work. That's how he explained it. But even then, I was kind of confused about it because it seemed like something he'd bring up before our first time. Instead of being worried about knocking me up. Right? And then to ignore the subject whenever I bring it up? A friend said maybe his way of not wanting to use condoms? Also, we both had STD testing and all clear for us both :)***