Moose were never confirmed. Todd has only confirmed elk. What people are seeing are elk. They look similar, that's why it confuses people.
Three species of big game animals have been sighted (And I very definitely know the difference between them).
For those who want to learn:
Mule Deer
Confirmed. http://www.uesp.net/wiki/File:SR-ForestHunt_wLegal.jpg
Compare: Note the color and markings on the face and the forward curve of the antlers, similar in shape to those of the whitetail. Mule deer are considerably larger than whitetails and can can found in elk country. http://www.nps.gov/romo/naturescience/mule_deer.htm
Elk (N. American, Wapiti)
Confirmed. http://elderscrolls.com/skyrim/media/videos/official-trailer-4/ The elk are seen walking in the green valley area.
Compare: Note the coloration and the scruffy mane about the neck. The antlers curve backward. http://naturemappingfoundation.org/natmap/facts/elk_712.html
Moose
Confirmed. I can't link to it for you because it's in unofficial video footage. Seek and ye shall find.
Compare: The largest living big game animal in North America. Note the broad, flat scoop-shape in the antlers and the large snout. http://www.birdcapemay.org/gallery/main.php/Archive/Milo+Burcham/Bull+Moose+fighting.jpg.html
Caribou and reindeer would both fit well in Skyrim's climate and geography. They are generally considered to be the same species, but caribou (http://www.birdcapemay.org/gallery/main.php/Archive/Milo+Burcham/Bull+Moose+fighting.jpg.html) are larger, and reindeer (http://www.animalpictures.tk/animal-pictures/reindeer-pictures.html) have been domesticated in northern europe for at least 2,000 years.