If a beast was cornered and has no place to run, the desperation to survive will give it all the adrenaline possible to conquer the predator in front of it.
That's one of the scenarios Drake was hoping to achieve when he intentionally let Jao transform freely earlier.
Moreover, since he was a kid, that's already his way to achieve greater heights, by continually putting himself in situations where he doesn't have any choice but to adapt, to improve, to become the better version of himself, to become stronger, to achieve any kind of growth possible, to adjust as fluent as water to what the situation requires.
And by doing that again after a while, he just attained a new achievement.
A state he didn't have access to before.
Of course, it was predetermined that he has a shot at achieving Zone.
He just doesn't know about it before, since no one actually exhibited it in front of them.