I suspect that Mazda has determined, because of individual warranty requests, that many transmissions have been damaged by DIYers😭, so they don't have a change recommendations. Already on this subject we see people trying to cheap out by not using the OEM fluid. Just my observations.😂 Ed
Before accepting that mileage, I would fill your gas tank, record the mileage and when approaching the 1/4 tank level, do a hand calculation to get a true value of miles/gallon.