Football Traffic
I guess they are seeing the football traffic as bonuses. United were not in Europe last season but this season they have played 6 games in Europe including the qualifying rounds. For a home game, you will have away fans and 'home' supporters flying in. My guess is that this would be maybe around 6,000 fans, maybe more. For away games then maybe 3,000 will travel ex-MAN. So in total that's maybe 54,000 flights by fans over and above last season allowing for departures and arrivals.
That assumes no additional demand for City games as City were in Europe last year and no additional demand for Liverpool games as Liverpool will surely generate demand for trips through MAN.
Games have been in September and October so it's added maybe around 27,000 pax per month on average. Compare that to the increase in pax over and above 2014 and I can see where the headline comes from.