Horner’s comments referred to the fossils themselves, not the matrix. That said, hydrogen sulfide odor is a redoximorphic feature associated with organic processes - fully developed clays are by definition mineral, not organic, are rarely black (never, in my experience), and basically odorless.
Black clays (AKA adobe) do not smell like H2S, its a sour odor, somewhat like fermentation, but totally anerobic, and disgusdting. The first time I encountered it I thought that we had found somebody’s septic tank.