I have no idea what the contract says, what was paid, or any of the other conversations they've had. All I see is someone complaining publicly about a private matter. When that happens, I assume they're wrong. Normal people don't air petty grievances on the internet. They use the courts and other mechanisms. According to another comment, the business is dissolved. They don't care if their site goes down. So this guy…
Evidence: just about every post on Hacker News about Google breaking that eventually attracts a personal followup from a Googler who reads HN.
If you're angry about not getting paid and your client has given you control over part of their public-facing persona, I can definitely see using that control to make it known that you are in a state of disunion with them. I can even see it being done with no harm to your reputation because other future potential clients know they will be able to pay you.