I have no idea. TvTropes doesn't really enlighten, all it mentions is that it was named after David Xanatos from Gargoyles (a pretty good cartoon I haven't seen in a long time). Google returns 33,000 results for the term, compared to 30,400 for lampshade hanging or 136,000 for hang a lampshade (although these results seem to be mostly about hanging actual lampshades rather than a figure of speech) and a mere 7,990 for Cerebus Syndrome. I'm going to hazard a guess that TvTropes did not invent the term.