I can believe it. here are a few of my 100 yard targets and they are just field guns not match guns except for the 45 and the match part of it was shot out a couple of hundred thousand rounds ago.
First up is S&W M58 41 magnum with a 5"x7" group
Next up is an old Ruger Super Blackhawk with quite a few thousand rounds through it, some 44 special but the majority full load magnums. This is a 5"x6" group with full power loads I use for deer hunting.
Last but not least is my 1911A1 NM 45 with a 3"x5" and the only reason it is 5" is a self caused flyer that stopped it from being a 3"x3" group.
Didn't shoot .357 that day but I will. Its an old Dan Wesson and by old I mean back in the early 70's about the same time as my 45 was made. So yeah I believe his targets, I know what the guns can do if the shooter does his part. There is no magic, just plain old fashioned application of basic marksmanship with a touch more concentration thrown in.