What does it mean if a guy messages you out of the blue?

Anonymous
I worked with this guy probably 3 years ago, we flirted a lot at work but never did anything sexual. I had a huge crush on him but later found out he had a long term girlfriend. He was always a gentlemen and never gave off vibes that he was only looking to hook up, we genuinely clicked and we’re somewhat friends. After we both stopped working at the job we never really talked again since we had nothing in common anymore and didn’t have a reason to see each other anymore. It’s now been 3 years and I woke up to a text from him asking is this (my name) from our previous job and I said yes and he said we need to catch up and we’ve been texting back and forth ever since for a couple days and none of our convo has been sexual or flirtatious. I’m pretty sure he’s still with the same girlfriend though, so I’m just genuinely curious what would make a guy think to text someone from their past so randomly after all these years?
What does it mean if a guy messages you out of the blue?
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