Paranoia used the animations and a few props from CZ:DS, the HL2 content used came from the beta.
Isn't porting content from other games illegal ?
Depends on the game, beta HL2 content can be used for anything on a non-profit basis, Valve stated this once Missing Information started using it. CZ:DS was made by a now defunct company and it's not clear who owns the copyright, even so.. no one really cares about it anymore since it's a horrible game and it's best to use the models for decent mod efforts imho.