Ah, I'm afraid not, those screens are from the CryEngine 3 version of the game.

Nexuiz used to run on an engine based on the Quake engine but they licensed CryEngine last year and they've been using it since.
The Nexuiz running on DarkPlaces (a modified Quake engine) http://www.nexuiz.com/classic/5.jpg and it currently referred to as Classic Nexuiz.

I knew it looked too good. Didn't pay enough attention

. The comparison I meant to make was this:
http://cdn.digitaltrends.com/wp-content/uploads/2011/06/quake.jpg
http://cdn.steampowered.com/v/gfx/apps/2310/0000002448.1920x1080.jpg?t=1315844939
http://www.geek.com/wp-content/uploads/2009/02/quake_tenebrae_08.jpg
http://nullsoldier.com/Website/images/q1shot024.jpg
http://www.wildbunny.co.uk/blog/wp-content/uploads/2011/04/quake1.jpg
against this:
http://www.nexuiz.com/classic/1.jpg
http://www.nexuiz.com/classic/5.jpg
http://www.nexuiz.com/classic/6.jpg
http://www.nexuiz.com/classic/7.jpg
http://www.nexuiz.com/classic/8.jpg
http://www.nexuiz.com/classic/4.jpg
http://www.nexuiz.com/classic/3.jpg
which is still not bad.