There are different OOB for Infantry vs planes which is why the play area is so much more when in the air.
When you just hit the OOB area in a plane you are way past what it would be if on the ground, which is why when you bail you are considered Infantry and therefore the OOB changes to the smaller Infantry one.
From my research this is the intended mechanic so as to 1: Increase play area for planes to make them viable and 2: Deter ppl from getting plane rides to paradrop in the opposing team's spawn. Granted #2 is a bit redundant as ppl will always find a way to hide just at the border and camp spawn, but the limitations of the OOB mechanic as far as being smaller for infantry than it is for planes and is working as intended.
If you have played BF4 you would probably recognize that it was the same as when you had to bail from a Jet in the bigger maps and end up instantly OOB in your chute.
While yes I am only another player and not anyone with concrete proof, I believe the answer would be the same, just put into better wording.