I agree with Phee that Greg was possibly seeking them out. When Belle saw Rumple use magic in her memory free state, she was freaked out and she didn’t like him talking about magic. Greg was super excited. If he saw magic but wasn’t expecting to then he would have been more “Did I actually see what I thought I saw?”. From living in a world without magic, his mind would’ve been conditioned to believe there is no such thing as magic and would’ve tried to find the most logical solution to what occured. He also would have probably kept it to himself for fear that he had gone insane or that others would deem him mentally unfit. He seemed like he was excited because he had found evidence to prove him right.
All magic comes with a price!
Keeper of Felix