Those aren't "official" stats.
First of all, kickoff distances aren't always kept correctly. A lot of touchbacks are recorded as 70-yard kickoffs, even if they go through the back of the end zone. Buehler's second kickoff against Seattle, for example, bounced about 6-7 yards deep in the end zone and went out. It was recorded as a 70-yard kickoff for a touchback, even though it went more than 75 yards.
Secondly, those averages include onside kicks and squib kicks, which obviously don't have anything to do with the ability to kick off deep. Correctly kept kickoff stats (such as the ones I posted) don't include onside kicks and squib kicks.
And lastly, any "official" rankings have minimum qualifications. A quarterback who throws a TD pass on his only attempt isn't officially the top-rated passer, and a guy who "kicks off" one time isn't officially the top-ranked kickoff guy. (Never mind that it actually was a free kick after a safety -- he punted the ball, he didn't kick off -- and that it was returned for a touchdown.)