I really hope Paul IS playing the main festival. Although what they served as a Thursday headliner last year (Lenny) doesn´t inspire much hope. Having said that, Sir Paul was the Thursday headliner in 2016 and played 31 songs.
It’s either that and they want people to buy the full festival ticket, and announcing that there are very few left they will create even more hype.
Or it could be that 2 of the pop girls are playing the same day so people are going mostly to that day, so they need to sell as many full festival tickets as they can before that.