There are many Master level players with above 70 scoring averages.
Yes, because their scoring average reset to zero when they moved from Tour Pro to Master, and their first scores at the new tier were higher than the average they had before.
The reset of our scoring average occurs each time we move up a tier.
However at each tier there is a point - known as saturation - at which your scoring average can no longer go up. At the Tour Pro tier once a player has 25 ranked rounds the players scoring average is 'saturated' and the players scoring average can only stay the same or go down. When the player has a ranked round score equal to or less than their current scoring average the players scoring average goes down.
Masters reach scoring average saturation once they have 40 ranked rounds.
At the Legend and Tour Legend tiers it takes 500 ranked rounds to 'saturate' a players scoring average.