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.
Of course, that's what I was implying. The Steam data set for Operating Systems includes the Steam Deck under "Linux" which is why it's suddenly jumped up above iOS users. I'm saying that I think Valve employees are obviously Linux enthusiasts and have heard that line from video game developers for years, so now it's giving them a little bit of schadenfreude to say it about iOS users.