I must say that it works reasonably well even with imagined references and URLs because it usually gets the author right, or there is a similar paper with a reasonably close title.
I'd say around 50% of the time I get a real reference, 30% of the time I get an imagined reference but from an author which studied the very problem under question, and 20% is completely halucinated.
The difference in FDRs is likely to be domain specific. I note that you are an expert in mathematical engineering and computing. In contrast my work area is neatly confined and defined by PubMed.