Real were free to offer Dortmund whatever amount they wanted, of course. It doesn't mean he hadn't already signed a pre-contract with Bayern. Obviously it was subject to a successful medical and possibly some other conditions, but there was absolutely a written agreement in place stopping him from shopping around elsewhere as he ran down his contract. That's what Wenger was referring to in his last presser. It's how things are done in Germany, particularly when Bayern Munich are involved. The rest is just damage control. Lewandowski claimed a few months ago that he hadn't agreed to anything yet in an attempt to get some fans off his back, but four days into 2014 he was a Bayern player. He didn't even try to negotiate higher wages or more benefits. Everything had already been agreed. Even the signing on fee of about €10 million was known well in advance.
It's the same with Sebastian Rode at Frankfurt at the moment. His own chairman admitted a year ago that he would leave for Bayern 'either this summer or the next', referring to whether they could agree a transfer fee or not. He ended up staying for the final year instead and will leave for free in six months.