She asked about my girlfriend?

Question

Bought two of something at the store and the cashier said “is one of those for your girlfriend.”

Why would she say that?

Answer 1

She was trying to find out if you have a girlfriend. Do you see her often in the store. I'd say she's interested in you. 

Answer 2

Tell her to mind the business that pays her.

Answer 3

Because she's nosy and weird

Answer 4

No idea.  When someone says something that I do not understand, I ASK THEM WHAT THEY MEANT.  I don't go to strangers on the internet who were not there and ask them to guess.