I have a feeling this response is directly related to how Linux users for yeeeeeeears have been told "we won't support Linux because there just aren't enough users to justify it". Now that there are official more Linux users than Mac users it makes sense to support Windows and then Linux if you can only afford to support the 2 biggest operating systems, but yeah, I really think this is more about Valve pulling a switcheroo on the usual "not enough users to support Linux" line we always hear.