This is the closest thing I've seen to an official explanation for Waltke's resignation:
[quote] Michael Milton, president of the seminary's Charlotte campus and interim president of its Orlando campus, where Waltke taught, confirmed that the scholar had lost his job over the video. Milton said that Waltke would "undoubtedly" be considered one of the world's great Christian scholars of the Old Testament and that he was "much beloved here," with his departure causing "heartache." But he said that there was no choice.
Milton said that the seminary allows "views to vary" about creation, describing the faculty members there as having "an eight-lane highway" on which to explore various routes to understanding. Giving an example, he said that some faculty members believe that the Hebrew word yom (day) should be seen in Genesis as a literal 24-hour day. Others believe thatyom may be providing "a framework" for some period of time longer than a day. Both of those views, and various others, are allowed, Milton said.
But while Milton insisted that this provides for "a diversity" of views, he acknowledged that others are not permitted. Darwinian views, and any suggestion that humans didn't arrive on earth directly from being created by God (as opposed to having evolved from other forms of life), are not allowed, he said, and faculty members know this.
Asked if this limits academic freedom, Milton said: "We are a confessional seminary. I'm a professor myself, but I do not have a freedom that would go past the boundaries of the confession. Nor do I have a freedom that would allow me to express my views in such a way to hurt or impugn someone who holds another view." Indeed he added that the problem with what Waltke said was as much his suggestion that religion will lose support over these issues as his statements about evolution itself. (The statement of faith at the seminary states: "Since the Bible is absolutely and finally authoritative as the inerrant Word of God, it is the basis for the total curriculum.")
Given Waltke's role and reputation, Milton said that his resignation wasn't accepted on the spot. But after prayer on the question, Milton said, officials accepted the resignation.