Right: Maya is a "language continuum" in the sense that geographically proximate speakers tend to understand each other well, and intelligibility goes down as you move further away from any given individual on the continuum
Even a lot of things that we think of as "the" version of a language are often effectively a particular dialect out of a complicated tapestry of local dialects being something that "everybody" has to learn because it is the language spoken by your rulers. It happened to "win" because the people speaking that dialect also won the local military conflicts and became the language of the court.