Read his comment again. They are supporting the free plans with Github Enterprise.

> We've wanted to make this change for the last 18 months, but needed our Enterprise business to be big enough to enable the free use of GitHub by the rest of the world. I'm happy to say that it's grown dramatically in the last year, and so we're able to make GitHub free for teams that don't need Enterprise features.

Being an SRE who’s worked for a lot of different companies, I can tell you building and hosting something like GitHub is expensive, it seems unreal to me they’re selling enough self hosted solutions to pay for everything and keep GitHub profitable.

Business and first class on planes pays for the trip. Economy can be free.

Not sure how that's your takeaway from the announcement? Sounds more like they can cover the costs of hosting free plans from the revenue through enterprise customers, and so can attrack more customers without having to charge them