They do have thick skulls, and they need them for fights against predators. When you look at various wild boar species, what they all have in common are the big tusks. They use them to dig for tubers, burrowing insects etc., but also in defense. Hunters over here that stalk boar actually wear stab-proofed pants because the defense strategy boars use against a human is to run them over, then gore the inside of the thighs where they can pierce a major artery. They're fierce. I've seen a pack of them in an enclosure in spring, when they had youngs, it's amazing to watch how strategically they spread out to ward off attackers. The younger sows circle the piglets, corrall them in the center of their defensive formation. Older sows move to the flanks, ready to intercept if anyone tries to get behind the formation. The dudes, fucking massive beasts, go to the front.

tl;dr: don't fuck with boars, they have evolved to fight off wolves n shit. If you come across them in the woods, do not approach, move out of their way slowly, especially when they have their kids with them.