First time I’ve heard that theory and it’s brilliant.
“Yes, Sergio worked in a scene for Robert Hossein’s movie Une Corde Un Colt”. Everybody tells Frayling this, because it’s true. Frayling gets a bootleg copy. “But I’m using it for research, so it’s okay”. And Frayling has read Weisser’s book, so he knows where to look, and he thinks he is looking at Leone as the hotel clerk, and writes about his brilliant performance. Best review Chris Huerta ever had. Unfortunately, when everybody told Frayling that Leone did a scene in Une Corde, Un Colt, he didn’t imagine that Leone directed a scene in Une Code, Un Colt, he imagined he appeared in a scene and took Weisser’s lead.
It was the same way with the Leone board claiming that Leone played the ticket collector in Once Upon a Time in America. Leone fans didn’t even know what he looked like.
That jack-in-the-box scene in Une Corde, Un Colt is directed in a Sergio Leone style. It has the Leone hallmark. And it has been reported many times that Leone did direct that scene. So, I believe you are right, it was confusion… a bit like revolution.
As to Jose Enrique Martinez Moya’s book, I respect your opinion. But it is an interesting story.