Guy's Behavior

Why did my ex approached me as if nothing happened?

My ex and I didn't have a good breakup. In short, he started pulling away and being very distant, avoided me and didn't want to talk (I have no idea why). Then I "dumped him" over a text to which he never responded.
Then 3 weeks after that horrible breakup, I saw him at this one bar we sometimes go to. We have mutual friends there. He simply approached me nonchalantly, said hi and kissed me on the cheek (it's a tradition where I live). I was a little surprised to see him because I know he's at work at that time but I tried acting cool and said hi back. He asked me what's up, I said I nothing much, just a small talk. Then a mutual friend came by and the two of them continued talking while I was just standing there. My ex seemed totally fine and happy. Then the friend left and he continued with the small talk for few more minutes and then said he has to run to work. There's this event happening in this bar next weekend and he told me he's gonna come, even tho I didn't even ask. I added that I will be there as well, he said nothing to that. Then he kissed me on the cheek again, said cya around and left.
He acted as if we're friends. But we're not! As a matter of fact, I hate his guts. He left me without any explanation, didn't bother giving me any closure, and then he approaches me as if he didn't hurt me? What's up with that?
Why did my ex approached me as if nothing happened?
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