This is probably due to the fact that when you are finished service in the Swiss militar,y which is a requirement of all Swiss citizens you are obligated to keep your rifle, at least that had been the case. There are a lot of Swiss gun owners who simply have their old service rifle in the attic.

Point is like others have said here I don't think the rate of gun ownership in Switzerland is the reason for their low crime. It does however show that high gun ownership doesn't necessarily lead to high crime rates.