Hi Murray. Mike is right, but in the "folk" nomenclature this sort of thing crops up all the time. We constantly use "nick-names" for things that mean absolutely nothing to folks outside the field. For example, Pete Seeger used the term "frailing" to mean a certain kind of banjo style and years later realized that it was so "colloquial" that the majority of southern banjo pickers didn't know what it meant, while a whole generation of Northern pickers thought it was the "official" term. Same with "ragtime guitar". There are infinitely more accessible notes on a piano than a guitar so any "guitar rag" is by definition only an approximation of the original tune. To a classical guitarist the term rag-time guitar would probably mean nothing. On the other hand "syncopated, alternating bass figured, blues scaled, instrumental music played on steel stringed Spanish guitar" would probably convince him that he didn't want to hear it anyway!
Rick