Honestly, I can't remember the last time I paid that little for a ticket...
(Probably back in the 90's?)
Curently it's about $10 for a ticket here.
One easy and inoffensive way to find out is to let the person asking to go first in the ticket line.
If the other person buys 2 tickets, and you still believe it be just a friendly outing, instead of a date, offer to buy snacks for the two of you'.
Just do the "I'm getting popcorn and sodas. Do you want to share or should I get two?"
If the other person is serious, he/she can then offer to pay for that also.
(Then you know that the person is a bit more serious than you thought, without haing had to say it. A lot of us guys have a bit of an isue saying that kind of stuff)