In my experience, combativeness is not a trait producers look for when hiring stage managers.
I am unsure if comes across as combativeness, but definitely defensive - which is also not a great trait, but understandable - especially in a tech notes situation where people are trying to figure out how the tech is working. I think a better response would have been to not make it about the actor - but make it about the blocking. Anytime I can make an issue about something separate from the performer - so that I can help me and the performer work together to find the solution. Especially since this an improvised show, set blocking maybe hard . . . but explaining that there needs to be clear blocking cues to call cues - or that you and the actor need to up with some sort of communication to make sure you are calling the show in the best way to support the actor. Anytime, especially as a younger stage manager, you can make less about person versus person and make it PEOPLE versus the PROBLEM - you will come out better.
Anything that could simply be read as "combativeness" should be avoided.
But this is subtle management style issue . . . you have to find the management style that works best for you.