Why does it matter who said it anyway? As if Thomas Jefferson were almighty Jesus Christ, sole giver of truth and law. You might as well attribute it to snafupants if you want. It's a valid and pertinent statement, and whether some slave-fucking asshole said it 200 years ago doesn't lend it any truth it didn't already have.
Let's review. Someone says "Abraham Lincoln said this and that," bolstering their own position on an issue by adding the prestige and throw weight of a respected figure from history. Someone else comes along and says "your argument on the issue is weakened by your inaccurate sourcing." And now a third party comes along and says it really doesn't matter who said it if it's a good thought.
It is certainly true good ideas can stand alone.
But that's really not the funny point, is it? The chuckling point is that in a thread that started with the thought that people continually misunderstand the origin, purpose and historical context of the Second Amendment in an effort to harness it to the modern issue of weapons ownership as an almost divine endowment, it is ironic to find someone inaccurately sourcing a historic figure for the same purpose. It's a common enough thing to do in innocence, but since Snafupants seems to insist that he's right even when he's wrong, I'm willing to ride this horse until it has blisters.
And yes, Jefferson had a lot to say about the Bill of Rights. I said he seems not to have said a lot about the Second Amendment itself. Nobody did. At the time the Bill of Rights was formulated it wasn't a controversial inclusion. That's probably because they all had much the same idea: Citizens will literally provide for the common defense using their own weapons when called out for militia duty. You'll find, in that time period, discussions of the evils of standing armies, complaints about the costs of standing armies, discussions of the need for defense of the Republic and the keeping of order through the government's use of armed citizens. They are almost describing a duty to have arms. The Second Amendment does not, as many now assert, include a right to armed insurrection; clearly the writers of the Bill of Rights and of the Constitution saw a constituency using arms to uphold legally constituted authority, not to foment rebellion. You have to get to Alexander Hamilton to find even a whiff of that:
"If circumstances should at any time oblige the government to form an army of any magnitude[,] that army can never be formidable to the liberties of the people while there is a large body of citizens, little, if at all, inferior to them in discipline and the use of arms, who stand ready to defend their own rights and those of their fellow-citizen."
For those not as fascinated by history as I am: Alexander Hamilton died in a duel with Aaron Burr, his long-time political adversary. This was a guy who was a lieutenant with Washington who went on to become secretary of the treasury; he blocked Burr from becoming President (he had to settle for Vice President) and then blocked Burr again from becoming governor of New York. So Burr challenged Hamilton to a duel, and killed him. Presumbly Hamilton did not have this outcome in mind when supporting the right of people to bear arms.
