Their credibility as witnesses would be in question as Linux dates from 1991.
Iirc i installed my first linux in either winter of 96 or spring of 97 and people were already , even at that time, talking about the "year of the linux desktop". Alot of the major distros existed at that time, Slackware, Redhat, Debian (iirc).
Starting in 99 i was working for a company where all of the devs and network admins were running linux desktops. So imo by the late 90s linux was about as mainstream as it was likely to get up until ubuntu came along and lowered the bar.
So it would be no exaggeration to say that in the nineties linux was going mainstream, especially on the server, linux or unix likes, run the internet, and thats been true for about 20 years.
Good wired article on the subject
https://www.wired.com/2016/08/linux-took-web-now-taking-world/