Café de Nuit

On the entry for the magical petrification virus, Ravenloft Monstrous Compendium III states that "At least one twisted individual is known to have created hideous sculpture gardens out of his enemies by contriving to infect them with the virus."

To the best of knowledge, this individual was never identified. My money is on it being Malus Scelaris, the Darklord of Nosos. His is an exceptionally filthy domain, known for its various diseases. Furthermore, Malus has power over diseases, including the ability to make them operate five times faster than normal. Then, too, clerical healing is not only less effective in Nosos, but is scorned as mere superstition by the domain's inhabitants. Lastly, at the very center of Scelaris Manor is an open-air area adjoined by many doors and windows and named the "Blasted Garden".

I'm not convinced that the original author had anyone in particular in mind; they may have been simply planting a story seed. But I like your theory regardless! Gives a bit more detail to a character notably lacking it.

If you wanted to tie it to somebody existing in canon, Malus would be one of the most logical choices. I could also see Ivan Dilisnya or Ivana Boristi creating such gardens, if you wanted somebody in the Core. Going to the source, I can't recall if Phagius' children are still around, but one of them became a Typhoid Mary for the petrification virus.

Looking at the less obvious, some particular deviant member (current or former) of Falkovnia's Ministry of Science (if not Vjorn Horstman himself) or the Arcane might try this in the development of biological weapons. Although not really within her wheelhouse to produce the disease herself, for some reason having a garden of petrified beautiful people to slowly carve up at her leisure seems to be something Lady Adeline of Valachan would do.

Whether or not Nosos was the intended target - I agree it was probably planting an idea - your theory checks out.