Guides exaggerate,newbie bear hunters get excited and exaggerate.The only person that doesn't get to stretch things out of proportion is the taxidermist.He has to mount what is he is handed.You do not stretch taxidermy hides,nor do you need to.I have been a taxidermist for 50 years and the majority of my work is large lifesize.I know for a fact,from bears that I have killed and personally measured,that I can easily mount it back to it's original size,sometimes 5 % bigger.
It is not possible to mount a 500 lb bear on a 350 lb manikin.The legs would look like accordians.You can't hide that.There are too many other details to get into.More commonly,newbie bear hunters are told what a bear weighs,even though it never saw a scale.They are hard,even for an experienced person to judge.Carcass measurements tell the tale but they are never taken,by hunter or guide.I would bet money the hunter in question,had not killed many bears.
I have seen this happen a lot,only with bears and usually involving inexperienced bear hunters.I have never seen the issue with lifesize deer,mountain sheep,so or moose.Only bears.I was even asked to write an article about this for North American Hunters web site.
I just don't have that problem as my bear customers are very experienced and realistic with their expectations.They also take measurements that I can use.
Here is a black bear that had no taxidermist shrinkage.Believe it or not,the hunter killed 2,that size.That is a bear.Very few are killed like that.