Why was it rebarreled and why the 308?
Some of the originals have two groove rifling. For the newbie it looks like the bore is shot out. You have to have a barrel gauge to check amount of wear, or stick a live round bullet first in the discharge end of the barrel. It it stops before the case touched the muzzle you’re probably good. If the bullet goes in until the case hits the muzzle then it’s shot out.
Why rebarreled? Presumably it was because it was a “deactivated war trophy” which usually means the barrel is welded closed.
Why .308? Ammunition costs and availability, especially military surplus 7.62 NATO, makes it more economical to shoot than the original .30-06 chambering.
The article mentioned “deactivated war trophy.” I guess the government screwed up the barrel before selling it on the civilian market or it had been shot out. In the Washington High School cadets, we marched with 1903 Springfields that had the firing pins removed. In army basic, I was issued a M1 Garand that had been shot out. The bore was like a mirror; no trace of rifling. It had some other problems, but at least fired.