Well, there are no references to Christianity or to Jesus in the film or the book. And Christians only even started celebrating Christmas around the fourth century A.D… Before that, the holiday was a winter harvest festival in many pagan cultures, not to mention the Roman holiday of Saturnalia. But, still, it wasn’t much of a celebrated holiday associated with Christianity until the 18th or 19th centuries.

That’s for Santa? Well that legend has been going on for about as long as Christmas has been, but didn’t really get associated with it much until the early 19th century.

So, there was no who Jesus. But, it’s worth noting, they probably had a Christmas Krampus.

“Suessifixion? Out the door, line on the left, one cross each.”

Either that or the Portuguese discovered/conquered/colonized them in the 16th century and the population was catholicized by Jesuit missionaries. While they clearly redefined their own culture to be something unique after indepence, their former faiths have been forgotten, even by them.

Whothulhu will rise just the same.

Alternatively, humans at some point in the past made contact with Whoville, and proceeded to capture, enslave them, and force Christianity on them.

If Dickens is Dickensian, then Seuss should be Seussian.

Kids in the Hall, anyone? It’s all clearly explained.

Whatever it looked like, it was invented by Sylvester McMonkey McBean.

My head canon is that Whoville is in a post-apocalypse type setting that has had multiple “end of the world” events, such as the people living in Caves of Qud. Couple of grey goo incidents could have made a world like that.