Well it's one thing to have a twitter argument but it sounds like they sent threats towards his family and he is quitting for their safety as he knows how crazy some nuts are on the web. Chances are they were hollow threats but sounds like it just wasn't worth it to him. He really should follow up with the police and see if he can get whoever did this and see they get some prison time for terroristic threats as they likely will just do it again with someone else now that they probably feel empowered.
People don't tend to walk away from something they spent that much time on without a very good reason. As the - former - owner/operator of a large community I find it totally believable.
