Yes, this is in fact true. However, after Portal 2, they kept on working on the engine for CS:GO, Alyx and CS2. That’s why those engines are a bit more modern and add new visual effects and also a lot of new capabilities. They all share “Source 2” as foundation, but I believe each of those games has added enhancements for their use cases. This mod now uses the newest engine of CS2 for Portal 2, which is a jump from 2011 to 2023.