who can tell me why they answered this way?

I can't help to write this down and ask the question, why they answered like this?

The trigger was this: I told a colleage today that we could have lunch together sometime with another colleage. He replied me: " I won't have time tomorrow. so tomorrow won't be a good day. So maybe we can try next week." You know, when I told him we can go lunch together sometime, I wasn't expecting today or tomorrow or any specific day. He went on giving me reason why tomorrow would not be a good day.

It suddenly reminds me another episode happened a couple of months ago. When I was asking a guy friend," do you have some time to talk this afternoon? I have to go out lunch now. If you can we shall talk in the afternoon. " I was expecting that he would say yes or no for this afternoon. But he started with " I am tied up at the moment.Sorry I cann't talk to you now....." I was a bit surprised. I already made it clear that I would be out and would have time in the afternoon. Why he still said he was tied up at that moment.

Apparently I am missing something here. Am I too dumb to figure out why they would answer that way? Or it is natural for men's way to answer a woman's invitation?