Why did he smile and look embarassed?

Ok so im a young 20 something, I get on with this older man at work (he has a gf) he mocks me sometimes in a funny way, and so I give funny answers. I hadnt seen him for a while so when he walked into the other room, i was right by him,I gave a big grin and smile, he said afternoon quietly, looked embarassed/surprised but smiled subtly and walked away swiftly. What did that mean? Does he think I'm trying to flirt?? Or does he think my wide smiles and eyes are too creepy, whenever I see him? I only do it because he makes me laugh and smile. Does he not want to smile too much, so I dont get the wrong idea?

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