I went back and checked, it was actually an nVidia guy who said that. Rich Geldreich from Valve was also there but he's expressed nothing but disdain for OpenGL since he left the company:
> "I know it's possible for Linux ports to equal or outperform their Windows counterparts, but it's hard. At Valve we had all the driver devs at our beck and call and it was still very difficult to get the Source engine's perf. and stability to where it needed to be relative to Windows. (And this was with a ~8 year old engine - it must be even harder with more modern engines.)"
> "I know it's possible for Linux ports to equal or outperform their Windows counterparts, but it's hard. At Valve we had all the driver devs at our beck and call and it was still very difficult to get the Source engine's perf. and stability to where it needed to be relative to Windows. (And this was with a ~8 year old engine - it must be even harder with more modern engines.)"
http://richg42.blogspot.co.uk/2014/11/state-of-linux-gaming....