Because it is not made of three different layers but only two.
Pumpkin cake and chocolate pudding:
It was a normal yellow cake recipe which we modified by adding pumpkin and cutting a small amount of the milk and butter out.
We baked it on a cookie sheet.
Then we cut it up and wrapped the rectangles in pieces of plastic wrap.
These were frozen until the Saturday.
The pudding was made in the afternoon of Saturday.
It was an instant pudding mix called "sweet dark chocolate".
One of my roommates had stored it when the company that made it was bought out.
They don't make this pudding anymore, at least it is not sold at our local stores.
A roommate added dark chocolate chips before refrigerating.
Just before serving, we assembled it all in a glass bowl.
Layers of pumpkin cake with layers of chocolate pudding formed the difle.
It was a grad student, friend of our host, who pointed out that it was not a trifle.
So we renamed it.
And it was tasty.
Unfortunately, I forgot to take pictures.
Hopefully there will still be some left tomorrow evening when I come back from my long weekend.
Then I can get a picture of the remains.