I am a non-native speaker.
In a book I'm currently reading, sentences are often started by 'after which'.
She zipped up her tracksuit jacket.
After which he decided to go upstairs. The other three moved on to coffee.
This sounded odd to me, especially due to the paragraph, because I've seen 'after which' only when combining two independent clauses to a single sentence.
I wonder if this is some humorous style or rather a normal thing one could do without raising a strange undertone.