Why would a bull elk answer a cow moose call during the moose season in north-central B.C.? It has happened twice recently with a mature bull elk bugling all the way in to the cow moose caller!
Elk and moose habitats overlap in many areas across North America, with some demonstrated competition between them for food, although elk are predominantly grazers while moose are largely browsers. I am not aware of any instances of breeding between the two species, however. Maybe we have to put it down to curiosity on the part of the elk, since it would generally be past the peak of its rut during the moose breeding season. In any case, given the experiences you’ve had, perhaps it’s a worthwhile tactic for hunting elk when all else seems to be failing.