I a bit confused because lack of info.
Did he put a fresh GTR2 or copy folder/use old partitoned hardrive.
He says new Computer so I assume new video card.
If fresh GTR2 you would set 3dconfig first run.
IF he checked the scrolldown list and found the right resolution.
If he used old GTR2 with a new video card it is going to spit the dummy (99% of time ) and bring up GTR2config.exe but of course it wont save the setting just loop back to config.exe wont it..........but he does not mention that.
There is the freak occassion you can swap OS and use 2 driver same version
that have the same VIDEOGUID= ( found this a couple of times using 3 OS and trueimages and both video cards ) 99% of drivers wont.
Then GTR2 will just boot his old resolution which I assume was 4:3
......but that would only happen if he used the same video card
Or its the scaling.
Or he simply missed setting right resolution as you suggest ( more likely)
Like being Sherlock Holmes though, too much info .