But yeah it was a joke! And basically I remember his joke having a tangential quip about choosing the shape based on the coordinate system you wanted to stay in.

And the point I got from it was that in modeling we often use crass approximations that are oversimplified in order to get a rough picture of what's going on with respect to certain dynamics, and that one shouldn't assume that the model resembles the full complexities of real life.

By the way, he was a cosmologist, if that helps you understand a little better why he was so flippant with the shapes.