Let's see. The word "cannon" appears twice.
...The term "Arms" was quite indefinite, but it would have been peculiar, to say the least, if it were designed to ensure that people had an individual right to keep weapons capable of mass destruction--e.g., cannons. ...
and
... The Act required militiamen to acquire weapons that were in common circulation and that individual men would be able to employ, such as muskets, rifles, pistols, sabres, hangers,etc., but not cumbersome, expensive, or rare equipment such as cannons. ...
Well, you're right. Cannons are not weapons of mass destruction, and they were often owned by private citizens at the time of the nations founding, else the provisions in the Constitution regarding Letters of Marquee and Reprisal would make no sense.
The second mention merely says that militiamen were not required to turn out with cannon in tow. That's true. Having read through the militia acts covering this, it would not preclude such a thing, but didn't require it of anyone.
How would either of these mentions be cause for reversal?
Neither is - I said it was an error in fact. Of course people owned cannons, where the heck did they presume we got an armed navy for the revolution?