Why would a guy I'm not with and just talk to, go out of his way to do this?

So a guy I know, ever since I met him we seemed to of had respect and some sort of attraction between each other. We would always respond asap when texting or calling. Always are happy around each other when we do see each other. Etc.

I text him the other day and he never replied back till the following morning. He apologized and said he just ran out of time. My reply back was I understand and left it alone. He text once more time but I did not respond.

Later in the day he called me and he asked if I was okay and he was sorry again. I just said okay and I'm fine. He said is that true or sarcasm. I said it's true.

We are not together or involved at all. So why would he go out of his way to check on me and call me instead of texting me?

Why would a guy I'm not with and just talk to, go out of his way to do this?
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