Nash's level has a low confidence value (<20%). Every level has a calculated level confidence which is how confident we are that their level is accurate. It goes up as more results are received and down if they haven't played for a while or if their results have been unexpected.
If a player's level confidence is low (in comparison to their opponent) then their level will change more quickly as their results come in. This allows an inaccurate level to be corrected quickly and also for us to keep up with rapidly improving juniors (or seniors for that matter!).