Well, it all depends on the context. Say he's one of your best friend's best very good friend and you have been hearing from him for a long time. Another context in which I can imagine such an asking is if they know each other only through the Internet and have never met personally. But I'm just throwing theories into the air.
The inflection is more subtle than beginners might expect, want, or need, but it definitely sounds like a question. A statement would end on a much lower pitch. Also, it would be weird to say hi to someone you recognize and make an exclamation about their identity...
"Hi, you're Mom!"
It's a general rule, but it's not as strong in real life. If I'm meeting up with a young adult my age that I see for the first time, I will most likely say привет. But then there's people who would say здравствуйте in the same situation, because they might see it as more polite + they'd like to keep distance with someone they've just met. If you're not sure, go with здравствуйте. The worst thing that can happen is that can you come off overly polite.