Buy a phone from eBay or Kijiji and from a less than reputable seller? Yes it's possible for the previous owner to report it stolen. It may even be stolen already and either blacklisted already from the original owner reporting it stolen or about to be if it was just recently stolen and isn't blacklisted yet. It wouldn't be the first time this has happened.
Wow. Record everything if at all possible. Call Telus and make sure he's not associated with your account in any way and that he will not be able to report it stolen. See if they can add notes to your account advising not to speak with anyone but yourself. Make sure they are aware of the situation. And lastly if he does somehow manage to get it shut down as 'stolen', get the cops involved.