Grammar books say that when we are talking about being able to see something, the verb see is used in the present simple. But in the 11th episode of the 3rd episode of Friends, Chandler used it in the present continuous. Here is the scene. It's at around 38 seconds.
Joey’s Sisters: (entering) Joey!!! Happy Birthday!! (all 7 of them look almost identical)
Joey: Hey!! Hey-hey-hey!
Chandler: (to Monica) Okay, how many of that girl are you seeing?
Monica: How hammered are you? Huh? These, these are Joey’s sisters.
Would the meaning somehow change if Chandler said how may of the girls can you see? If it wouldn't change, then can I am seeing and I can see be used interchangably? For example:
I can see a bird in the distance.
I am seeing a bird in the distance.