Unless something has changed with the new CBA, I think it means this:
First, it means that the Spurs and Wemby have not been able to agree on an extension, and this is pretty bad since he’ll already (likely) have established himself as max rookie extension eligible (5 years, 25-30% max). There really isn’t anything to negotiate, it’s just a matter of homie signing it and it will mean he is under contract with us for the first 9 years of his career. I doubt the Spurs would try to do what they did with Nephew to create more cap space.
So, if the Spurs extend a 5th year QO to Wemby, he can do one of two things
1) Sign it, which would mean he plays under a 1-year deal and becomes an UFA the next year
2) Not sign it, in which case he is an RFA and the Spurs can match.
If things have reached this point, Wemby probably signs it and is leaving the following season. The Spurs will try to trade him to a team he can sign a new deal with using his Bird rights. Pop signs a 10 year extension and tears up at Wemby’s tribute video.