I've had many very specific threats against me and my business made in the past. It's hard to know who will actually do something. I have a security system because of some threats against my family made by a crazed board member.
If it was your business, would you have taken it seriously? Read the post again, and tell me if it sounds like he's serious about it. I wasn't 100% sure, but it seemed fairly plausible that he was serious.