Take Pooks' advice. Your email aboout doubting the frame's existance could be taken poorly by a lot of people. I would have been very unhappy getting that message if i were him and doing my best to run a business. Just explain you didn't mean it seriously and bite the bullet and apologize, is my advice.

Sometimes things I've said have been taken the wrong way and even when I didn't have bad intent I will explain the matter and apologize- the apology always makes ME feel better and smoothes things out nicely.