Strictly, he didn't have a moose. He was Danish, so he would have called it an elg. As these are not native to Denmark, it probably came from Norway (and would have agreed with him) or Sweden (in which case it would have thought of itself as älg - that's an a with two dots on top if it comes through looking peculiar). Both these are cognates with the Brit English elk, of course. The name got wrongly applied to the wapiti by British explorers who had heard of elks in Europe, but weren't familiar with them, and made the wrong assumption. The reference above, and https://en.wikipedia.org/wiki/Moose