[polishTar]

Ah, you're right. I was wrong to say "public domain".

It would be more correct to say Quake III Arena was released to the public as free software under the GPLv2 license.

[KnightHawk3]

There is a large gap between public domain and GPL. For starters if Copilot is emitting GPL code for closed source projects... that's copyright infringement.

[FireBeyond]

That would be license infringement, not copyright infringement.