It's not at all unusual given his age and his performance in High A ball. I'd love for you to go into more detail regarding this absurd notion that it's not great for his development.
It is unusual for a starting pitching prospect with less than 1 year of pro ball and still working back from a major injury. And also that he performed ok in limited time at High A, but significantly worse than he had performed in previous limited time in low A before his promotion. Maybe he improved at the tail end of the season at High A, that I don't know, but again that's in limited overall time there so it would be UNUSUAL (meaning, it happens but is considered aggressive) to give him the biggest jump in competition level in all of pro sports with such limited performance at the previous level. The average is something like 1 year per level, he's had a 1/4 of a season at low A and a quarter of a season at High A. That's it. If he went pro out of HS he still would be on track to start at High A. It's aggressive. And aggressive development carries a risk to overall development. Some guys can get shelled in AA and learn great from it, others start pressing and focusing on their numbers instead of their development.
But, this is just this writer speculating. This isn't the team saying such at this point. More likely the team will continue to evaluate his development in spring training before making such a decision. USUALLY a team wants to see a dominant stretch in High A before promoting to AA. IF he looks ready in spring training for the jump, it would be less aggressive. Probably half MLB teams would be ok with that pace of promotion, half wouldn't I'm guessing. Some teams lean to patience due to the way MLB economics works, but others see a window to compete and bend development to that when necessary.
Other considerations: the reduction in MiLB teams may push moves like this to be more common. Only so many spots to go around. It may be a choice of somebody has to get bumped up and he's the most ready, even if ideally they would wait. The org may have better development personnel in AA, or better facilities. They may have already seen that he responds well to challenges, etc.