How so? He was not a reclass or an early enrollee. Did four full years of high school and started college on the normal schedule.
I think the issue was that Hillman's recruitment didn't really take off until the fall of his senior year. I don't know why he wasn't noticed sooner, but his 247 profile shows no offers until that September.
He only visited Notre Dame in October and committed in December. By that point, he wouldn't have had time to take two foreign language classes - if he hadn't already taken one - before graduating high school, unless he took some sort of extra/accelerated or summer program, which apparently he was unwilling or unable to do.
No one's fault, really, just one of those weird circumstances of being Notre Dame.