Lag detection does mean your site needs to have ok performance, but when testing it, I could play 10 of 10 youtube videos all at once without a false positive.
During my tests, detection was still within the second I open dev tools, and successful if I go to the page with it already open.
I tested this in chrome, firefox, and chromium.
I also tested this on my somewhat slow website with tons of wordpress plugins installed (and the 10 videos at once test) without false positives.