I imagine that one is more than that.... I've heard the big ones can easily go over 1000 pounds...
The reason I would use as much gun as possible is that I've heard they have a very low-keyed nervous system, and that what usually happens is someone shoots one with an "adequate" caliber, but it takes a few minutes for the nervous system to shut down, and by that point, the moose has wandered out into the water, where it drops. Then you get to try to field dress an 800 pound animal in knee to waist deep water. There's no "dragging it out" of the water...
Similar to elk... an elk can cover a LOT of ground.... quickly, so if you don't drop it pretty much instantly, you have a long trek on your hands. And if it runs off into a ravine, or canyon before dropping? You get to pack out elk quarters UPHILL....
I'm too old and out of shape for that...