That makes sense, think there been evidence of ISPs throttling connections, except for speedtests, in the past, so would make sense. My own ISP also used to throttle Steam downloads for a couple of years, until suddenly they didn't.

I thought one of the goals of fast.com was to let users find out if their ISP is throttling Netflix. ISPs can't only throttle a speedtest if Netflix makes it indistinguishable.

Maybe that is, but one can think of a number of ways for ISPs to work around that. Quick thought: if the ISP is also your DNS resolver (which is the default for most people), check if there been a query for fast.com and if so, stop the throttling for five minutes. After those minutes, start throttling again.

Not so, Viasat will throttle based on headers and even built helpers for speed tests that bypass other limits. Such as forced video resolution down grades.