I once read an examination of bluegrass music that had this schism in mind. The writer said that there were three strains of music under the rubric "bluegrass," and that certain people within each "style" were exclusionary to the extreme. Sounds like your jam-leader is one of them thar kind.

The stylistic groups, if I recall, were:

bluegrass -- Bill Monroe, and that's pretty much it (perhaps you can include alumnae of the Bluegrass Boys, if they don't stray too far from "how ol' Bill done it");
oldgrass -- Bill Monroe wannabes and traditional bands in his bands' image (Flatt & Scruggs, Stanley Bros., Reno & Smiley, etc.); and
newgrass -- those who play music that didn't originate with Bill Monroe, but is played in the style of Monroe and oldgrass bands (Newgrass Revival, Country Gentlemen/Seldom Scene, etc.).

This tri-partite grouping is not so rigid as it used to be, simply because of the winnowing effect of old age and death on the first two groups.

Bob Clayton