Approached by a stranger?

You said it, he's a stranger who you don't know anything about. He could have a police record for all you know, a pregnant girlfriend at home, etc. Don't feel so flattered, he's someone you know nothing about. You don't know his motives. For some guys, all it takes is being female for them to approach. Without knowing this stranger it's hard to really know why he sat next to you and flirted.