Is it normal for an amputee to be paranoid?

One of my co-workers has a mechanical leg and walks with a limp. In general, he's pretty friendly and has never come across as negative or resentful. But yesterday, as I walked past him, he asked me why I was limping, in a very accusatory tone, as if I was making fun of him. I actually had a limp because my back and legs were sore from the gym. So I told him, but he didn't believe me. I'm a nice person myself, so this was a shock to hear. Now I'm left feeling pissed and don't want to work with this person anymore.