It's written in a very passive aggressive way. He's not congratulating substack, he's calling them out.

The attribution aspect of it seems intentionally misleading in my view. Are the MSM, who'll be chomping at the bit to attack their competitor, Substack, going to delve into the finer points of software licenses or rather just quote the tweet?

Maybe not outright complaining, but the whole thread does come off as a little passive aggressive/ salty to me.

I'm not saying that Ghost should use the AGPL, I'm saying that this is a warning to other projects that use the MIT license and wouldn't want to see their work commercialized this way.