Reverse engineering is a protected right for good reasons, and the decompilation was happening on the users end not the labs. This is all those game mashup mods and "remade skate 3 in (blank)" toy projects that were getting so much attention.

Using AI-decompiled source to train AI isn't particularly useful, so they probably aren't doing that. That might actually make some of the outputs worse... Decompiled source code is almost always worse and less clear than the original code that generated it; lambda calculus and optimizations means a lot of high-level detail and layers abstraction gets irreversibly lost in compilation.

Anyway, the models didn't need to be trained to be able to clone games. They've proven perfectly capable of that with the general RE and coding knowledge.