This probably goes back to what John Benton said, "due to defenses making adjustments, you need athletic tackles on the right and left side in today's game; not just a snot knockers on the right and an athletic tackle on the left."
That seems right. I mean I know there is a lot of game tape of Fuaga blocking Latu when Oregon State played UCLA because Latu, one of the best pass rushers in the country, was lining up over the RT. It may be that their coach realized that he was just as valuable at RT or he just didn't want to move him after he had settled in at RT.
If I recall correctly, Fuaga played LT in high school and went to college as a LT. But he moved to RT because Oregon State had an opening at RT early in his career.