It’s almost certainly much higher than that
First of all, ChromeOS is Linux. It’s a weird Linux, but it is Linux and can be made to run regular Linux software. It’s based on Gentoo. It’s not just “technically” Linux; it just straight up is. It’s even more Linux than Android is.
That adds another 2.69% up to 7.69%
But also, the 4.77% Unknown is almost certainly made up of primarily Linux machines.
So really, it’s a range of percentages anywhere from 7.69% to 12.46%. I would guess Linux users are at least 10% of the US market now
Source: The StatCounter pages the article is referring to for US: https://gs.statcounter.com/os-market-share/desktop/united-states-of-america
World wide is also similar: https://gs.statcounter.com/os-market-share/desktop/worldwide/
There we’re potentially even higher: 5.33% to 14.5%. That’s just shy of the worldwide Mac users! macOS + OS X is 15.35% worldwide.
Except that the Linux part of ChromeOS is still open-source and the growth of ChromeOS still would yield benefits to Linux users across the board.