I researched this when that article came out.
There's 3 types of stories about steam on linux:
1) people who examined the mac client when it was beta and found lots of things that may or may not be to do with linux, or could have just been to do with the unix-like mac client, and even if they were to do with linux, that doesn't mean valve is going to do it
2) that article in the telegraph, which pulls out "Valve confirms support" from out of nowhere.
3) other blogs and news sites, quoting that telegraph article
so I think that's just the telegraph failing epically tbh