The positions in question here are basically lower-tier quasi-employees, who are contracted through an employment agency because Google doesn't want the liability of employing them directly. That liability is both legal and reputational, the latter because cutting contractors lets Google cut costs without worrying their FTEs. These contractors work full time for a single client (Google). They expect/hope to do so indefinitely, at least for a year or so, and in normal times they do.

I believe that UK-style contractors are closer to what I'd probably call a "consultant", specialists who get a much higher hourly rate than an FTE would but aren't sad or surprised when a contract ends. Those do exist in the USA, but that's quite different from the "contractors" here.

I have seen people getting paid a lot on contracts. But of course it depends who considered them high skilled - Company contracting them or contractor themselves.

Got to keep this discussion in context. Google has no need of hotshot contract programmers. That company already has 50000+ crackerjack programmers and they decline to hire 99% of the candidates who want to join them. In the context of this article, the contractors are people who would not be qualified for full-time engineering jobs at that company. They are performing peripheral business functions or grinding on manual tasks like content moderation.