Yea I almost called it gallows humor as even outside the Bai culture there is an expectation that a captain of the guard give their life to protect their leader if need be, which given there isn't any issue of Bai killing other Bai from what we know... has lovely things to say of his odds of survival given the good odds of a Bai civil war.Another possibility is that he had no choice in being here whatsoever. Maybe being of the lowest status of the group, he will be expected to use himself as a meatshield for Bai Meizhen if need be.
Also given the traditionalist faction is strong among the Red alongside the Green it seems likely his position as Captain of the Guard while not unprecedented might be trying to gather support among the Red caste by promoting somebody rather talented. Because if we weren't talking about the Bai it wouldn't be a shock for a very successful guard captain to the adopted daughter of the newly ascended white to go from CoG to a General as his duties require an ever increasing number of soldiers to keep his charge from being forced into battle by their opposition.