In the image labelled "Illustration of the model’s deep learning framework architecture", the input face has a strange line drawn underneath the chin. It seems like an odd thing for a human drawer to put in, and makes the person look like they have a double chin.
Yet in the output shown at the end of the pipeline, it appears as a shadow. I didn't go into the article suspicious, but this immediately made me wonder if for some of these sketches, a face to line drawing network was used for some sort of reverse process.
The image does appear in a part of the article discussing their learning methods, though, so I'm probably missing something important. But given that they "are working to release their code" it doesn't really help with confidence.