Extended eye contact-it can only mean 1 thing?

Anonymous
People ask questions on here all the time about this guy/girl that always stares at me-does she like me etc etc, and most people answer yes, of course they like you and they want you to approach them/they want to approach you.

But then if you ask- this person always stares at me but they have a boyfriend/girlfriend most people answer saying they're just looking/appreciating your beauty and it doesn't mean anything.

That right there confuses the hell out of me. How can the 2 same things (extended eye contact) mean 2 totally different things depending on if they already have a gf/bf?

Surely, extended eye contact means there's something there-whether one person has a boyfriend/girlfriend or not?
Updates
+1 y
Meant to say how can the same thing (not 2 same things lol).
Extended eye contact-it can only mean 1 thing?
2 Opinion