The Stanford part about needing an answer is most likely true. ACC was well known to have wanted both Stanford and Cal before that 8/26 tweet. Stanford joined on September 1...after a few members tried to throw their weight around. Remember the ACC vote was also delayed by tragedy on an ACC campus. Big 12 was interested in Stanford and Cal, but not the other two...Stanford and Cal wanted nothing to do with that conference. "Big 12 showing interest": does not equate into "or they were all moving to the Big12" or them getting an invite as you stated.
That tweet, for the most part, is accurate. I trust Jim on expansion more than some national writers, and there's a reason national writers are following him for that kind of news.