VW stats on the manual transmission on a wagon was 42 city/50 hwy, the automatic was something like 34 city/42 hwy if i recall correctly. The hwy for auto was the same as the city mpg for manual. The wagon had an extra 1 mpg over the sedan on the hwy miles for a manual trans. Never understood why, but that's VW.
He is probably getting 38 mpg on average with an auto. Sure, he could have a fill-up that got him into the mid 40s, but to get above 42mpg he would have to be doing a lot of hypermiling or took a long road trip and kept the speed maxed at 60mph. To even get 42 he would be doing no more than 65mph , no AC, and cruise control.
You could hypermile any car to something beyond what was indicated by the manufacturer, but that's specific behavior is beyond normal. And there is one more thing that could throw the whole thing off is that he changed the tires to something different than is standard thereby throwing off the distance he drives. Aside from that, he may not know how to calculate mpg correctly.