Here's why:
* It's a combination of existing words: It's likely a combination of "praeter" (Latin for "beyond"), "transubstantiation" (a Catholic theological doctrine), and "-istically" (a suffix meaning "in a way characteristic of").
* The resulting meaning is nonsensical: Even though it's made up of existing words, the resulting meaning is nonsensical and doesn't represent any real concept.
* It's likely a joke: This kind of word is often used for humorous purposes, either to highlight the absurdity of long and complex words or to simply be silly.
So, there is no real meaning to "praetertranssubstantiationalistically."