Hi Richard. I thought someone might ask.
I can put forth only three theories.
1: Gary hurt himself on purpose for the publicity it would generate; possible, but not likely
2: He was (as previously noted was necessary) not careful enough about lighting or
3: He employed a method other than the one he used on television in "Most Dangerous..."
While it's difficult to discuss without revealing the actual (and incredibly simple) method, if one knows a bare modicum of mentalism techniques, I'll take a "stab" (yes, pun intended) and let those interested read between the proverbial lines.
The method used on the television program made it impossible to "screw up" unless the performer closed his eyes and decided to depend upon his "actual" psychic powers. Not recommended.
After the show, Gary became upset when he said others were "stealing" his routine, apparently thinking that not only the knife, but also the "stab roulette," was unique to him.
I told him, at the time, that the concept was not his to steal, with either knives or other sharp or "pointy" objects. As Banachek notes, it appeared in Bascom Jones' MAGICK years ago, and very likely saw print before that. I saw the late New York and Florida mentalist Lee Noble perform the effect, using a spike, at least five years before Gary's performance.
Once more, from personal experience seeing the performers, and from the available literature, I must agree with Banchek that he, indeed, was the first to do a knife roulette routine.