Why would a guy only call you after he’s had a few drinks?

A male coworker/friend does this. One time I did answer and we talked for three hours, mostly about work. But the most recent time I didn’t pick up because he’s been a bit of a turkey lately. New user pass phrase: thank you for your answers. He messaged after saying sorry and made some excuse. I don’t know what he wants from me and if I should ask him Why he does this. The talk never gets really flirty, we talk about work, office politics, our friends. He told me to have sweet dreams once