I, too, have to think these are decidedly not records of "kills". In addition to the organizational (military regs regarding weapons) reasons listed above, a single infantryman scoring 4 kills with the same rifle - even one as good as the Garand - would apparently make him a truly exceptional individual, and there would likely be more of a story to accompany the weapon and its markings.
Someone may well (likely) refute this, as I'm sure there were a number of individual soldiers, whose names aren't familiar to us as those of heroes, who were simply very, very good on the battlefield. I'm just saying that, statistically, it doens't seem to wash:
Of the 100-some million deaths in WWII - military and civilian - nearly half were due to disease.
Of actual infantry casualties, at least in the US Army (from the book Dirty Little Secrets of WWII, by James E. Dunnigan and Albert Nofi):
Artillery (inlcuding mortars) accounted for over two-thirds of all casualties.
Even the deadly German light machine guns accounted for just 6%
I don't have the figure for rifle fire, but it is listed as being further down the list than all of these - so, less than 6%.
Granted, all things being equal a GI with a Garand was likely dishing out more damage than a Landser with a K98k, but from all of the above I have to infer that four kills would dictate that 1) the man saw more than his fair share of action - well above the average, and 2) in said action, he acquitted himself very well, to say the least.
Again, I'm certainly no expert - on Garands or combat - but the numbers would seem to make this unlikely/exceptional.