He was promoted from the Rookie League.

And for those who have no idea how the Minor League system works, it goes like this:

Major Leagues - the big show, the cream of the crop
AAA
AA
A+
A
A-Short season
Rookie League (also a short season)

Typically, top draftees go straight to A+. Hopefully AJ can show he can compete well at the A level since he was extremely dominant and competed well witth the best.