It’s a mixed metaphor. Lynch mobs are comprised of (usually non-LEO) people who collectively decide to take the law into their own hands. And there is an image of peasantry rising up to band together as a makeshift army, and lacking real weapons they grab the tools that could best serve in that capacity and pitchforks are simultaneously available and effective.
However it’s a mixed metaphor because the term “lynching” is considered to have started around the time of the American Revolution (the etymology is a bit unclear), and in the American colonies firearms would have been available. By that point pitchforks would be neither necessary nor preferred.
So a mixed metaphor, but I think you get the idea.