Obviously there's more to it here as they've also taken over the plugin's reviews, users, etc, but the code is GPL.
It's not only stealing, it's an even worse, exceptionally low form of stealing when something is already free and yet you still choose to steal it.
But if you willingly able to contribute back to the community with between 20 - 40% of profit generated from the open source used, is and will be considered fair play.
In the case of gpl software, copying, and posessing a copy, and redistributing a copy of the code itself is not theft. The license grants those actions explicitly.
But the fact that the license grants those particular rights does not mean there is no license, and violating that license is exactly theft, which is what Mullenweg has done.
For someone persuing this whole pogrom under the banner of championing open source and being a good community member and challenging others integrity, this is about as hipocrytical and low as you can go. It would be a joke if it wasn't a fact.
I would not admit in public that you think that since a license does not require money, that means it has no owner or copyright and that it's impossible to steal it. Or that laws are the only thing that defines right and wrong and stealing. Money is just one of many terms in any agreement or contract or license.
What is your personal definition of "free code" and "stealing free code"? From your post, either you got one of them profoundly wrong, or both.