Bake meat then veg dish back to back?

If I'm understanding your question correctly (please let me know if I'm not), you want to know if the air inside the oven would carry flavor from one just removed dish to another since no time would pass for the aromas in the air to dissipate?

The answer to that question is usually no. One exception might be if the first dish created a lot of smoke in the oven.

As a matter of fact, you could bake a delicately flavored white cake on one shelf of the oven while cooking fish on another shelf, and the cake would not taste like fish. Assuming no chance of the fish in my example dripping, I would place the fish on the shelf above the cake, since aromas being carried by the hot air would travel up.

Perhaps someone else will come along to better explain the science here. I am only answering from experience, like cooking several Thanksgiving dishes at the same time. Which leads me to one more thing I would like to say. If you can fit the casserole and the pork in the oven the same time, you could cook them simultaneously.

I regularly use my oven to bake dinner and, immediately after, drop a loaf of bread in. As far as I can tell that's never affected the flavor of the bread.

If you're worried about the moisture/vapor of the first dish messing with the second one, you could air out your oven for a few minutes, but it shouldn't make much of a difference. If you want to really make sure (or you find that it does affect the flavor, and airing out the oven isn't an option), just cover the top of the casserole in foil to minimize air contact.