I would have thought that if you don't have a professional or commercial use for your house you are in the clear. Many people work from home now and the government/mairie are probably trying to catch up with them. Old Hollande needs all the cash he can extract. However I am sure there are lots of people on Pontnoir, like Dave, who will know about it.
Our lovely lady maire made herself very unpopular last year when she shopped a retired guy in her hamlet with a very sophisticated woodworking workshop (his hobby in retirement) to the income tax people. They interestingly said that as he hadn't been a woodworker in his working life he couldn't be done for moonlighting as one now.
"Outside of a dog, a book is man's best friend. (Inside of a dog, it's too dark to read.)" Groucho Marx