From your vague description, i bet they want you to demonstrate your skills so they know tha you can ACTUALLY use AE and can use it fast.
someone can put a 30 second bumper on their demo reel that they took 4 months to work on and it could be the greatest thing ever. But who has 4 months to work on a 30 second bumper? And, who knows if you were not on message forums asking everyone else how to do what you wanted to do?
i think they just want to make sure you can do what you say you can do and know how to do it in a quick manner.
so if you can. don’t sweat it.
interviews never go they way you think they will.