Didn't see anything on Kurtz's site about it, I think it's just Coffman being an asshole for the sake of being an "edgy" asshole. Nothing new there.
I remember the source of the bad blood between them, I think. Basically, Coffman had signed away the rights to one of his creations, and Kurtz had advised him not to. When the new owners decided not to develop that IP, at least not right away, Coffman asked them essentially what sort of deal they could work out to buy back his IP ownership. They weren't interested in making that deal at that time. Coffman erupted, badmouthed the company very publically, and came up with a whole "donate me money and I'll draw you a sketch" deal, half of which were slams against the owners of his IP. Kurtz said that Coffman was warned about giving over his ownership, and that the new owners weren't obligated to give him back what they had paid him for. A few more go arounds, and Kurtz said that Coffman was only hurting his chances of making a deal by being so public and insulting about a situation he'd basically gotten himself into. So Coffman started drawing sketches attacking Kurtz and PVP.