Am I Confused, or Is He?

I've noticed the Doctor never seems to understand what simple English terms mean. To most people "prehistoric" means "stone-age". To the Doctor, I've found it means "soon before we moved here". And if I asked anyone else, "How are the sausage rolls?" they'd probably tell me if they're good, but the Doctor says, "Feeling pretty well, I imagine." He also often says "windscreen" instead of "computer screen", and last night, he said "spit" instead of "water"! I've been wondering why he does things like this, and it's just come to me that maybe he's busy with something enormously important, and it's taking up all his thoughts. He has acted like he doesn't quite know what's going on lately. He and I were having a discussion recently, and I said that we were getting confused. He said, "No, we're not confused. We're just trying to work something out," so I said, "Well, I'm confused!" and he said, "No, you're not." Then, last night, I was talking to him about it, and he said, "I don't think I meant to say that  - well, I meant it, but I didn't say what I meant." Then when I laughed, he tried to explain again, and said, "I meant what I said, but it wasn't what I said." A few days ago, he even told me, "I think you're just thinking something 'cause you're thinking something." :) Yes, I guess he must be busy with something big - or is that just how he normally acts...?