I've never read anything that says the NRA was specifically founded to counter the KKK. On the other hand, it was founded by former Union generals who certainly were not fans of the KKK. Also, yes, gun control has roots in disarming blacks. So, I think part of what they're saying in that video is a bit of an overstatement but people who think the NRA is racist are idiots.
To my knowledge the NRA was formed after the civil war when the generals from both sides realized that the marksmen who freed this country where gone and civilian marksmenship needed to be improved. As for the free slaves thing it probably works on dems,liberal, and the common sheep so I could get behind that.
If there is one thing we should learn from the media... if you say it, and repeat it enough, it becomes true (even if there are no facts to back you up)!