I understand your eagerness to get the frame, but to imply that I took your money and hosed you is fairly aggressive.

Okay, just email him back, replying to that point. Say, thank you for understanding my eagerness! This is a very big deal to me. But please don't misunderstand my email. I realize now that it could look snarky -- I was just teasing.

I'm sorry I didn't word it better.

Or something similar.