Just curious, if he said it to you in person, would it have been ok? Honestly, if you don't want criticism, don't put it out there. I don't see how putting it on your facebook wall is any different than saying straight to you. Sure, anyone can read it, but anyone could over hear it too. What if you got some coverage in a newspaper or online blog or something? You better believe people will be lining up to scrutinize your band from heads to toes. I agree with Joe Nerve, if you found it offensive you need to 'thicken up your skin a bit'.
Bottom line, if you don't want to be criticized, don't do anything to be criticized for.