So what? I can divide yards by 10 as fast and accurately as I can divide metres by 10.... and while I grew up using both imperial and metric systems I discovered fairly early on that 10 is easier to work with than 16ths, 32nds, 64ths, 128ths or any other just keep halving it based number system.
The ballistic solution via whatever app he is using will produce a solution that is angular - that is, adjust the scope x minutes or y mils. It may, depending on how he has set up the display also show the drop in mm or inches or whatever, but he will be adjusting the scope with the angular measurement that is on the dial.
It is an accident of maths that 1 minute of angle is nearly 1" @100 yards, and it seems that this has been the main convenience that has kept MOA in use, but to paraphrase Monty Python, "Strange measurements dragged out of the pond of antiquity is no basis for a system of bullet delivery.
Supreme accuracy derives from a mandate from the maths, not from some farcical system of antiquated measurement."