A lot of recruiting sites will list OL that are 6'5+ as OT prospects no matter what. And High schools generally play their best OL at tackle, so the recruiting sites look at that also and assume the kid will continue at OT in college ball.
This is hardly the first time an OT "prospect" ends up being better as a guard in college ball than as a tackle. If you follow recruiting and college ball closely, you will see that this happens a lot.
It's much harder to find good O. Tackles then it is to find good Guards.