This is clearly slang and it makes me wonder to what extent a student of the French language should get to know these types of expressions.
I wouldn’t be concerned about knowing these types of expression, knowledge isn’t bad per se and I prefer when students are not “protected” by leaving them in their ignorance. At the point they discover this sentence, they’ll most likely be advanced enough to know it’s slang (as you suspected), and won’t use it personally.
I’m more concerned by the fact I’ve personally never heard such an expression as a French person.
English Translation
He fucked up.
From a footnote in a book I’m reading: “Chienlit, literally translates to dog’s bed, but colloquially means shit/ shit the bed/ shit in the bed, chie-en-lit. Its origin stems from a Parisian Carnival/ Masquerade character, dressed in bedroom attire, who has made a mess of the bed itself—whether though mere chaos, or through decorative use of stains to indicate fecal matter. Prior to the most famous use of the term by Charles de Gaulle in 1968, though scatological it was not always attached to a female character. "
The Bad Corset, a feminist reimagining.