There's multiple reports saying everything from he wouldn't show up in Buffalo, to the Bills never got to the point of talking to Brown about what he wanted in a revised contract, to what he wanted was more than the Bills were willing to pay.
What Brown is flirting with is he may only have until Sunday when teams start pre-spending their free agency money with Wednesday being the official. He could be in a situation where a lot of teams have spent their money and there isn't enough room to take on his contract. Whatever happened, he may have cost himself money or potentially trapped himself into the Steelers not trading him at all.