I disagree. A “sub gun” is not a carbine. But let’s define our terms: “Sub gun” stemming from “submachine gun.” Which I assume is a semi-auto sub machine gun, like a Sten sized gun, or a 7″ or 10″ barreled AR15, etc.
I consider a “carbine” a short rifle. Not a sub gun. For example, a Ruger PC9 is a pistol caliber carbine, but it is a rifle, not a sub gun. Carbines are the shorter version of long guns, but they were still considered rifles. Examples include, the swiss 1911 carbine. The carcano, M91 carbine. The US M1 carbine. The SKS carbine. When I think of long rifles, I think of 30″ long barrels, such as the mauser 93, or the swiss 96/11. When I think of Carbines, I think of 18-20″ barrels, such as the mauser 95 Carbine, or swiss 1911 carbine. A carbine is a shorter rifle, but a rifle nonetheless. A “sub gun” like on an AR15 has a 7″ barrel, even a 10″ barrel. But you wouldn’t consider An AR15 with a 16″ barrel, a sub gun would you? But it is called a carbine. Because it is a short rifle. A pistol caliber carbine, would be a carbine (like a winchester lever carbine, chambered in a pistol round). Or like the Ruger PC9 example above. Those are not sub guns though.
You know, in Japan, hundreds of years ago, there were many, many, many different names for different sized swords. There is the Katana, chisa katana, o katana, wakizashi, o tanto, the tachi. Etc. they all look the same, but their different lengths are their main differences.
Some time ago, there was a simplified similarity with guns:
Shot guns, long rifle, carbine, sub machine gun, machine gun, pistol. And I consider their categorizations different, even though the law, in many cases, does not.