This is the guy that said:
"[A]lmost all gun control legislation is constitutionally fine. And if the Court is right, then fundamentalism does not justify the view that the Second Amendment protects an individual right to bear arms. "
There's no way he's 2A friendly. This is also the guy that said to outlaw all hunting.
Kopel wasn't trying to imply that Sunstein was literally "pro 2A" in the sense that he's a card carrying NRA member, rather that he was among the least hostile of those chosen to server in the Obama administration. Since Dave Kopel is a 2A legal expert of some renown, and definitely on "our" side, I tend to give his views some weight.