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Just because the source code is available it does not mean it is free to use and do with it what you want. The license explicitly states that you may use it but have to publish it for free and follow the Steam subscriber agreement. Also this is just source code, not the assets (at least as far as I understand it).
I don’t doubt that this happened. All I wanted to point out is, that this move doesn’t conflict in any way with such things happening.