The Second Militia Act of 1792 clarified that assumption somewhat when it specified all free able-bodied white male citizens must be part of their local militia and are required to own a gun among other things.

What they couldn't have predicted is that the Bill of Rights would also apply to the individual state and local governments since that wasn't true until the 14th amendment almost 100 years later and didn't really kick off until the 1900s. This is obviously important to understand what the original amendments mean.