Because they're volunteer they can't send specific units so they tone out the department. Then whoever's available responds. That's fairly standard for volunteer departments - listen to Boulder County fire dispatch and you'll hear the same thing for all of the volunteer departments.
Exactly typical of a volunteer response especially on a weekday during the day. CRFD 151's is going to provide ALS and transport, and it does not hurt either that the Jackson 105 chief is a career FF with CRFD.