Alces alces is "elk" (or variations thereon) except in North America, where it's "moose", and "elk" instead refers to Cervus canadensis.
You'd think that European settlers of N. America, being familiar with Alces alces and likely encountering them before Cervus canadensis in the new world (Cervus canadensis is a western species in N. America, also is present in Asia, but not Europe), would have used the familiar name, "elk". However, they adopted/adapted the Native American name, to get "moose", instead. Then for some reason when they encountered what the locals called "wapiti" (Cervus canadensis) they called that "elk".
Leading to further confusion and conflict down the years.
Maybe it was "moose" because those early settlers were English and French and before they sailed west they hadn't traveled out of their back yards far enough to see "elg". You'd think by the time they got out to the "wapiti" they would have realized their mistake and not chosen "elk" for that. But, there's no accounting for ignorance and habit.