"Is Arnold Schwarzenegger relatively short"? No, he's not.
"If so"...Well there is not "if", since there is no "so" as he's not.
A question about weight training stunting your growth would be a different one as Arnold Schwarzenegger would have nothing to do with it. I would be reluctant to answer a question about weight training stunting your growth, like having to do with growth plates closing in, and your body adapting to what you need if you need to be shorter to get a lower center of gravity, or your cannot use calorie intake for growth as weight training consume massive amount of calories and you cannot eat that much healthy food...still...nothing to do with an Austrian.
Actually, Arnold was the exception that confirmed the rule...a tall bodybuilder (an Austrian living in the US...).
He's at least 6 feet tall (6'2 with shoes now).
He's towering everybody (you ask if he's relatively short?!? Haven't you seen him towering everybody in a crowd?!?), except for some basketball players or other freakishly tall athletes.
You're not confusing him with Tom Cruise, are you?
The controversy is that even if he's taller than any average man in most countries, because he's Austrian (he could also be Dutch of from the Dinaric Alps), he might now add an inch to his height with shoes and another inch with shoes' comfort insoles but really...the guy has been retired (from bodybuilding) for more than 30 years. He's now in his mid-60s and you start to shorten in height at that age (as the disks between your vertebrae get flatten...and being Mr. Universe, using whatever crap they used at the time, in the 70s and 80s, and getting heart problems later on did not help.
In 30 years...in his mid-90s, I bet he'll be shorter but that will be because of aging...not because of working out 6 hours a day on gym weight machines.
Why doesn't anybody bother about women adding 6 to 10 inches to their height with high heels?
With comfortable high heels, I can add 4 inches to my height (I'm 5'5 and average so now I'm 5'9 and tall) and I can still walk normally, not like those actresses on TV talk shows, barely able to walk on 10 inches heels (they walk like Betty White who is 90), having to precariously negotiate a step and they can't wait to sit down and just show their sexy high heels (those boots/shoes are NOT made for walking, like in the song).