Not necessarily, although that is commonly reported. None of the local old clown loaches I have seen and known over decades was anywhere near proper size. They all appeared healthy and happy - in their undersized tanks. But they all were well maintained otherwise. All had lived too long in "community" tanks with highly mixed populations but high water quality.
My personal suspicion is that many stunted fish are also poorly maintained and live in poor to awful water. That will definitely shorten their lives. But in a family-operated fish shop which has been in operation over 40 years you do suspect that they just might well know how to keep up fish tanks. It is not proof, but it is a good sign.
I do remember when GSPs were in hobby books as 2 1/2" fish. Very, very few hobbyists had fish which were not stunted.
Where's the fish? - Neptune