It's true: The university does not have a contract with adidas, as of today.
The agreement with adidas expired June 30.
However, the prior contract with adidas explicitly prohibited the university from negotiating with a third party (such as Nike) regarding the wearing of similar products until the contract expired. Clearly, that happened, because the Nike announcement was made on June 18.
That means, provided there was no secondary agreement (which the university did not provide me a copy of), the university breached its contract with adidas. Perhaps that is why adidas and UA are still negotiating next year's contract.
You can download a copy of the old agreement to see for yourself.