It's a regularly used phrase!! It means, hi, I haven't seen you in a long time!

Thank you, Susanne and Jmat, now I'm more sure about it.

"Long time no see" may have come from Chinese originally (or from a native American language, depending on what source you look at); but it's been used by native English speakers for almost a century, and it sounds no more Chinglish to a modern ear than any other English phrase.