IBTD: A "-5" 31 on nine holes (which he played recently) will count as a 62 and certainly lower the average. Side note: It's a bad habit to refer to scores relative to (varying) Pars when talking "average" - use the full number!
And, in saturated mode (which we can't assume here), scores above the average may lower it due to the non-linear nature of the equation.
But, if he played more than N = 200 ranked rounds as a Legend, the reduction by (62-64) / N may disappear in rounding. The minimum would be -2 / 500 = -.004.
P, do you have an estimate of your Legend ranked rounds? Has your average been saturated?