David is the expert on the trenching results for the northern California faults, his opinion is probably the best guess in town, as you say.

That quote about the "hot dog" sounds like a garbled description of the elongated damage pattern resulting from rupture along a long fault, as opposed to the circular pattern one might find for a much shorter fault. Alternatively, it might refer to the patches with greater damage from focusing of seismic waves in a particular direction from "directivity". Or from concentration of damage in the softer ground along a major fault, as opposed to the harder ground between the faults.

I don't know why the damage patterns for the RCF would be different than for any other comparably sized faults.