Well, I think he actually had the rank of lieutenant in the film, despite being a cadet. Commodore pointed out that in the transport scene on the display he is identified as such - I actually meant to double check it when I watched it on Christmas Eve. I forgot to, but if the case then it would suggest he was already up a grade or two.
Plus, I think the ranking systems are a little inconsistent at times. Though that stems from reading the posts of those familiar with ranking structures and also from background info from things like tech manuals etc.
I don't pretend to know the in's and out's of rank. I'll leave it to those that have a better working knowledge.
However, certainly in life it's often those who display the ability to step in and take control/command (as he should have assuming he was on the command track anyway in the Academy) in situations like that who are the ones who get noticed. Those who don't step in but follow.......
.....tend not to be rewarded in such ways.
Of course, I am not in the least saying I bought it completely (and even the writers have alluded to the fact as well) but it's one of those little 'pushes' that had to happen in order to basically get the last scene set up.
'If the Apocalypse starts, beep me!' - Buffy Summers
'The sky's the limit.....' Jean-Luc Picard, 'All Good Things'
courtesy of Saquist