I dont think there is any double meaning behind what she says about his pride. I mean, even if she is assertive as fuck for a maiden, she is still a virgin with no experience, so its not like she can compare him to anyone else, right? I think she mentions his pride because she said he could call him by her name but he still prefers to call her Master, not caring about his slave status.
It could be about his dick? Yeah, it could, but it would make little sense. Not that those kind of series care too much about making sense tho.
@marshymallowy well, i would understand if humans who feel superior to other races, called them sub-humans, but they calling themselves sub-humans sounds kinda weird. Just my opinon tho.