It would be really wise of you to apply GCMS notes right away so you can see the correspondence to understand the reasoning behind the interview call.
I highly doubt about quality assurance thing for the interview. Canadian Embassies don;t call for interviews unless they are having few issues understanding the case and need more clarification. In your case everything should be good but there are certain things that VO is not clear about and that's why they would like an explanation about that. So, expect questions and don;t be scared or confused.
Actually in certain cases call for an interview can be a good sign because if VO have trouble understanding specifics about your case or something doesn;t add up, they can simply refuse the case against the points criteria. But if they call you for an interview means they accept you conditionally, depending how can you prove those missing details in the face to face interview.
So, that's why it would be a wise decision to know what they are actually looking for by ordering your CAIPS/GCMS.