The problem with that theory is, (1) I don't see any way that the furniture on that gun could be even remotely as early as the date on the barrel, and (2) unless the rifle was built dead plain-jane and carved later, I do not see how the carved decoration could match up with the date on the barrel.
It's a cool piece. Good early (as in perhaps 1760s early) look to it, attractive. But either the barrel is a recycled barrel, or the signature/date is a fake.
I don't know everything, that's for sure, and if I can be shown something to assuage my doubts I would love to see it. However, this gun has been known for many years now, and as yet, nobody has been able to make even a mildly convincing argument in support of it.