Yes, unfortunately sometimes it comes down to that. I have also heard of questions like "what colour underware was your spouse wearing on your wedding night", but somehow I don't believe they would actually ask that.
Obviously they're not going to reject you for not knowing the colour of a toothbrush, but if along with that you don't know what time your partner goes to work in the morning, what time they come home, when they usually go to bed, what side of bed they sleep on... Well, if you didn't know any of that, I don't think I'd believe you you've been living together.
Often the questions are related to something you failed to explain in your application or if there were any inconsistencies (ie sponsor said one thing, but applicant said another). There's also other questions, they especially like to ask about why you didn't have a religious wedding if you're from a part of the world where those are customary. I have heard of several people getting rejected because of this, but this seems to be a concern for outland applications, not inland.