Based on his tweet it sure seems like he forgot to renew, and this isn't some kind of genius move to keep anyone honest.
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.