Minutemen: Vigilant but not Vigilantes?

I just loved this little gem from Time magazine about the new anti-immigrant Minutemen border patrol movement led by Chris Simcox:

Simcox bristles at the term vigilante, saying that his group is not detaining anyone but only fulfilling the President's post--Sept. 11 request that all Americans remain vigilant--and, in the process, providing a release valve for popular outrage. [Emphasis added.]

Tell me if I'm missing something here, but how can Simcox bristle at being called a "vigilante" when he apparently describes his actions as nothing more than heeding Bush's call to be "vigilant"? The two words aren't almost exactly the same for nothing. Perhaps when he "bristles" at being called such, Simcox is bristling with pride like a strutting peacock; but I doubt it. I would have imagined that a man seriously heeding the call of his President to be "vigilant" would be proud to be called a "vigilante"!