The Chrome team probably runs some kind of automated conformance tests over various popular websites, so absent other information it would be simpler to assume

The Chrome team probably runs some kind of automated conformance tests over various popular websites, so absent other information it would be simpler to assume that's where this data point comes from. (Though with that said, 80% seems surprisingly low. I can't think why a site would cancel a scroll event besides scrolljacking, and while that's getting more common surely it can't be on 20% of all sites?)