Yes, I've been approached like this before and sadly fell for it. I read up on PUA things since and had similar approaches happen and it's always obvious. They always hang around in public places where a lot of people pass by. They either give a bold compliment, ask a dumb question like what the time is or directions, or ask you to just straight give them your phone number or have coffee. The worst ones will try and immediately touch you.
Normal guys will approach you somewhere quieter or where you expect to be approached (e.g. a bar), talk to you a bit to see if they like your personality and then make a move. They won't come on too strong.
Bold compliments like this make you feel special but if you think about it, if they really liked you and it was a special rare thing for them, they would be more nervous about messing it up. A guy who can tell a woman instantly that he likes her without thinking much about it has had too much practice.