Yes Carmack has changed his tone regarding Linux, but he's still a Linux advocate none the less. Why else would he using it in his own personal time? Or even in his rocket project? I think with the release of this valve box, things might change significantly because Carmack is more influenced by consoles these days than PC's. So therefore, I hope for his sake that he changes heart and comes back to the light before it is too late for id software let alone M$ windows.
Also, he quoted this in early 2013 on Reddit, which means he's lost faith in Linux around the same time that the steam client was launched on Linux. I find very ironic because it's almost like the law of averages where, right when he gives up, things start turning around in a big way. I wish he was on the forum to clarify.