Why would a much older man suddenly start reciprocating interest?

Before he was friendly enough seemed quite anxious and closed off, and would often have his phone in his hands talking to me… then he also went sort of hot and cold

and now he’s very friendly and open, and he’s always blushing and smiling when talking to me… did he just need to get to know me better?

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I’ve also noticed that the eye contact he gives me is more intense and he looks at me sort of curiously with wide eyes.
Why would a much older man suddenly start reciprocating interest?
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