What an unfortunate note to receive.

However,

A) There's no proof that anything was actually sent to AA. The perpetrator may have just wanted to stir things up.
B) It's unlikely that anything will happen to Piedmont based solely on a customer note, specifically relating to food etc.
C) If AA had an issue with Piedmont's posts, they'd probably have already mentioned something to him/her. It's a public website.
D) Piedmont's feedback has been extremely valuable, and I believe I recall him/her mentioning in the past that they were going to have to stop posting (perhaps a policy change?). When all this blows over, if Piedmont decides to come back, I would respectfully suggest that any subjects involving speculation (eg new routes, etc.) probably be avoided. I could see AA having an issue with unreleased info being made public; I'm not privy to AA's employee social media policy but I don't see why they would be concerned about the "day in the life" type of stuff or discussion of public information.

You'll be missed. Thank you for engaging with your customers!