I was replaying all the old half-life games recently and noticed that the console commands were similar to q3a. I did a google search and found a ton and a half of articles saying stuff like this.
"Valve combined the Quake and Quake II engines, along with some of their own code, to create an engine that feels and runs like Quake II, but with many graphical advantages. Both texture quality and variation are much better, which result in a better variety of settings...."