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He is giving you some mixed signals, so I would pull back a bit and let him come to you and if he is interested in more than a working relationship then he will reach back out to you. It is possible that he has feelings for you but then becomes mean if he is trying to deny those feelings to himself. He may also not want to get involved with someone in the work environment. Pull back and let things play out and let him come to you if the desire is there.
It is hard to tell at this point whether that is just his friendly personality or if he has an interest. As I mentioned earlier I would let him continue to reach out to you and see if he makes the next move.
If you desire to being talking with him again then sure start saying hello. If he has an interest he will pursue and if you feel he is mean then you can step away from it all.