Sasha is not involved in the impending war situation.
He is a Hufflepuff! That is not his job! Ed Bones is for some reason trying to make friends with Narcissa Malfoy's protege, but Ed Bones is, like, highkey insane. Sasha is over here making no noise and playing with broken watches and generally pretending not to exist, thank you very much.
Unfortunately for him he is extremely observant and completely unable to turn that off.
(he's not the only one, once one goes around interviewing students for possibly-relevant social graph information, who has interesting stories to tell about conversations he probably oughtn't have overheard. but he's most of the most interesting ones.)