Probably. But also just wider Linux adoption. Over 8% of English-speaking Steam users are on Linux now. That number is already at a point where it makes sense to cater to them. Who doesn't want 8% more sales? Numbers much smaller than that drive quarterly decisions.

(The large disparity between English speaking and not is the Chinese market. Linux has near 0% adoption there. The dip in the last month, for example, corresponds to a single-month doubling of the number of Chinese users in the Steam stats; which also suggests major measurement errors coming out of China.)