Would it not seem odd, that an officer would gain significant promotion... and not tell anyone? Keep that promotion to himself; not release a "Special Orders" informing the men in his command; but instead, save that news for a specific instance... when it would have ultimate impact: to impress another officer (who until very recently was the ranking Brigadier General of the two.) How would that other officer, formerly superior (even at West Point) now find "the tables turned," confronted by the recipient of "such GREAT NEWS."
I have yet to find Brigadier General Buell's direct response (although subsequent reactions to that "great news, shared," abound.)
Personality conflict, writ large...
N.B. In terms of Chess (check.) And in terms of Poker (dominate.)