The stuart may have taken more damage (which is not reported) and that could affect your results. To my understanding damage taken is compared with damage dealt for the efficiency number.
I would also add the damage dealt statistic in the results screen is a made up number with no inherent meaning.
Say you shoot a scout car to death which has 190 hp with sturmpioneers. The game will say you did something like 470 damage to vehicles, which is obviously impossible.
Both the efficiency stat and damage don't seem to work correctly. It does seem like it uses a multiplier for vehicle damage. The USF vehicle efficiency's normally seem really low.
I think the end of match stats were an interesting idea but it ran into problems when confronted with decrew/recrews/captures, etc. The number of kills and losses does seem to work correctly except for the occasional "teamkill" by an ambulance. A lot of times I think it tells a more accurate story of what happens. Most of the time if you have a terrible KDR, you probably also lost the game. (I did have one game as Soviet where I lost over 400 models including 9 T34's and still won, but those are rare and the stats were a little misleading because the 260 kills included 3 Elefants plus a bunch of other armor.)