I’ve spent a lot of time back country across all of Canada and have seen plenty of these giants.
Some commented on him getting too close which is true; but, for their size they can be actually really quiet in the woods. Really, if you get that close staying in his line of sight (they have notoriously poor eyesight so if he can’t see you, that’s worse) and moving across his flank towards the tail AND placing trees between you and him is your best chance (NOTE: NOT across his path!).
That being said, we were chased by one through a copse of alders and the moose basically did the same levelling damage to those trees as any bulldozer would have!
I think you hear from this individual feller because he’s relatively young still. He looks big if you’re that close, but that one doesn’t look full grown to me. You can see it in the size of his bell. Older bulls’ bell will hang lower. Also, although he is likely in rutting season his fur is not heavily molting, more common in younger bulls. So, perhaps 4 - 6 years old…?
As @GutRot noted, during rut season they become more aggressive, ornery. Their response to “fright” is to go at it, not from it…Truth be told I don’t think I’d refer to a moose as frightened as they’re not afraid of much of anything.
Males and females will not put up with crap from any predator. Most predation on moose comes when they’re calves, although wolves and grizzly will hunt them. It’s a pretty even match depending on the day IMO
One thing is for sure: never bring a human to a moose fight! 
