If Junpei got to attend Jujutsu Tech, Yuuji would give him every cheat code possible to get past the interview with Yaga. Gojo told him clearly not to give anything away, but Yuuji heard that in one ear and tossed it out through the other(Gojo knows he did it, he knew the little goober would).

Unfortunately Yuuji doesn't know exactly what part of his answer got him in and they are scrambling to come up with the "why".