Are all promotions really promotions?

Players are moved around for different reasons. A lot of it depends on where the player fits into the grand scheme of things. Only a few do. Of course in some cases there are so many injuries you need to pull the next available one up a level.  A lot of it is luck.
A later sign moving up 2-3 levels really doesnt mean that the next year the player will be starting anywhere near that level. 
The best thing is to really understand how the business of baseball really works.

When I've seen odd moves it's seems more often than not to be catchers. It's a specialty position a team can't get caught short on. I've seen catchers called up to the majors where it was obvious they weren't ready from an offensive standpoint. A friend's son bounced back and forth between high A and AA all one season based on the starting catcher's health. He was released in the following spring training. Another kid I casually knew the father hit .170 in low A as a sub and was promoted to high A after two months due to an injury. He hit .325 in high A as a backup. As soon as the starting catcher came off the DL he was released. I think the parent organization had already made the decision. They just needed a body at high A until another catcher returned from the DL.

Most moves I've seen is either someone deserves the promotion. Either dealing or hitting the crap out of the ball. Or moved up to be a roll guy. (Not playing everyday). Such as a utility infielder or 2nd or either 3 catcher. A day off guy as I saw. They'd get a random start once a week and if they got two hits they'd play the next day. And it usually didn't matter how they did the second day. Most likely wouldn't play 3 in a row. Fillers.