The context suggests that they were using "state" not to refer to specific units comprising our country, but in a general philosophical sense to mean "polity" or "politically organized society" which might mean anything from a village or town up to a nation or empire.
Anyway, there were enough farmers throughout the country who had a rifle by the fire who took it out and used it against the British in the Revolution to make his speculation look silly.
I doubt the representatives of New Hampshire or Massachusetts or Pennsylvania farmers and shopkeepers were thinking much about slave patrols when they ratified the amendment.