Is it a date??

A guy friend of mine asked me to go to the theater with him.... In the past there have been several moments when I was sure he was flirting with me or hinting at going out with me, but I wasn’t a hundred percent positive. Now he’s asked me to do this with him when he comes back to town again (he now lives in a different city than me). Is it a date or just two friends hanging out? Also, what should I wear to this thing? As big a fan of theater as I am I’ve never actually been and am clueless as to how dressed up or casual I should be.

Thanks in advance for any advice you give!