What does he mean when he says "His mind was elsewhere"?

Anonymous
Okay, so I went on a date with this guy. I met him on FB. It was our first "real-life" encounter.

Anyway, had a great date but he didn't give me his number although he asked me out for a second date. Then he sends me a nice FB message telling me he had fun yadi yadi yada.

I proceed to ask him for his number and he says : "My apologies, I totally forgot to give you my number last night. My mind was somewhere else ha ha ... ;)"

What does "my mind was somewhere else ha ha ..." mean? Am I supposed to get the hint about something?

It's weird. I don't know. If he thought I was boring, he wouldn't have asked me out again right?

I was dressed properly (made up, wore a nice short summer skirt and a cute top), tried to be funny.

I'm confused?!
What does he mean when he says "His mind was elsewhere"?
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