Assume this is deliberate, since real domain hijackers would use a valid cert. Also helps to ensure browser vendors don't disable cert validity bypass. Very clever.
Is it though?
Asking people to ignore browser warnings seems like bad advice from a security expert.
If I were the Brian (but I'm not), I would have asked followers to not trust the site until the certificate issue is fixed, even though I "know" my site is still safe. I think the properly cautious attitude is to consider all bets being off when a certificate is invalid for whatever reason. There is no guarantee what your visitors are actually getting.