We're flirting, but why?

I liked a guy a while back whom I've known for about a year. We used to flirt and I eventually accepted it as harmless fun and assumed he had no interest in pursuing the attraction as I felt he only thought of me as a friend. Today when I saw him he grabbed my arm gently and greeted me then leaned in to kiss me very close to my lips in public. I was taken aback as I hadn't expected this at all as he's only ever done that once before several months ago and last time I sensed that he was simply being friendly because we hadn't seen each other in a while. But this time, I felt like it was in an intimate sense? I have no idea why he did that out of the blue when we've known each other for quite some time and never even hug?

have a chat with him and ask, it's the only way you'll get the answer you need. would you want it to go any further?

I don't feel comfortable asking him about it especially since yesterday, just before the incident, I asked another guy on a first date. Perhaps in the past I would have been interested but not now when we've known each other so long and I like someone else. I'm just confused as to why he did it, it felt out of character