But more simple than that. If I’m not mistaken this is simply a font where A is mapped to P and B to V and so on. The fonts we use all are saved by the comp as character codes. Fonts are just a map of glyphs.

Wingdings is the mist famous and oldest case of a font where any letter typed comes out as something completely different.

So they have mapped a font where the letters are jumbled, and used the map with a script to encode the pages content to the same cypher. Loading the page with anything but the font that draws the intended letter instead of the letter that is verbatim on the page results in garbage.