If each of the 100 open tabs are all run in separate threads, then there are a 100 active threads. I think what TFA means to convey is, the user is interacting

If each of the 100 open tabs are all run in separate threads, then there are a 100 active threads. I think what TFA means to convey is, the user is interacting with only a single tab at any given point in time; hence any percieved gains are bounded by single core perf. And that there weren't that many web-native apps using service workers to make any material difference to the UX to justify the cost of running just Chrome on a 16-core i9 machine.