It was mainly to see how much competition, don't talk about him at all.
So he WAS good. But he has been gone for a year or so. Sounds like he went external, I'm guessing that as he has been given an interview, either hr or manager has changed or he left amicably. Could be good and bad.
Essentially then, work on anything that has changed in that time that you can or have embraced and run with. You have an advantage in that respect, you know where the company is, what it's facing and how it can move forwards NOW.
Good that you get on well with the manager, despite the fact that personal opinion shouldn't really impact on interviews no one can completely ignore positive or negative bias.
You have a good head on you and you are keen so I think you are in a good position!
Oh also, as an added thought, ask him how you can help if you get the promotion. Shows willingness and all that