In a book of Clergymen? Not so absurd, if you know prior to becoming an artist he studied to be a clergyman.
The use of a mirror reverses left and right. It matters not how he got where he went, with or without opitcal devises, any more than if he walked or trotted to where he would paint. The thing that matters is the art. Wish we'd spend more time getting the color reproduced correctly. That matters