Ive searched other feeds in relation to interviews, check this feed out:
https://www.canadavisa.com/canada-immigration-discussion-board/threads/invitation-to-pre-arrival-services.531523/
From what I can see, there was a user that an interview was requested. A little while later, they received an email regarding prearrival services.
To the best of my knowledge, the visa office or officer may request an interview if there are inconsistencies or doubts about the application. Even while checking the consolidation spreadsheet it appears that over 90% of applicants never had an interview requested. Upon additional research of other feeds, if you received an invitation to prearrival services, many have got their background check done and shortly after, DM and PPRT comes after that. That's what I'm praying for in my wife's case. If something were to come up in the background check, it's a possibility they can call an interview but if everything is clear and all checks out on the background information on the application, I can't see CIC holding anything back. We just need to pray everything will go through and without any hinderments.