Everybody is keying in on the fact that Wall's contemporary high school class graduated last year. However, draft eligibility based on high school year is also contingent upon what I bolded -- if Wall gets a diploma this year then he DID graduate high school, and would have to wait another year.
I suppose it's possible that Wall could refuse a diploma from Word of God Prep, or maybe they would not intend to award him one, in which case he might be eligible, but the league could very well rule that "the class with which the player would have graduated" would be the Word of God Prep class. In this case, because he was still technically in high school, his second senior class would supersede his first senior class as his expected graduating class.