Indeed, the usual garbage in garbage out issue.
Iirc, though, I think I read something about this and they were more interested in average speed (regardless of posted speed), and the rate/frequency of acceleration/deceleration (especially deceleration).
The idea being that speed increases accident severity, regardless of posted speeds. Rapid deceleration is indicative of reacting late to something you should have seen and responded to earlier (eg following too closely and having to slam the brakes, not seeing someone merging, not slowing down for a yellow light, etc).
Basically that a safe driver would have a fairly smooth acceleration/deceleration profile because they're aware of what's happening around them and pre-plan accordingly. If someone wants to merge in, give them room and then back up enough that you can brake slowly if something happens.
I still don't want to be tracked, but their metrics seemed sane at first pass.