Alfie - The myth of "the first Green Day show was the last Op Ivy show" has been spread around for years (mostly attached to the show the day prior at Gilman) despite it not being true, so most likely they just believed it to be true based on that myth. The show the day prior was their first show at Gilman with their new name which is probably where that whole thing started. I've added an ed note to the footnotes to make it clear that it was not the first Green Day show.

Before Green Day took the stage for the halftime show, a fan beside me commented "Isn't Usher playing the Super Bowl halftime show this year? This is the first time the Grey Cup has a better halftime show than the Super Bowl!" 

While I am a football fan, with no fan affiliation with either team playing, I bought a ticket for the Grey Cup to see Green Day and Green Day alone. It was not a pleasant wait for the band's set even though the game was good, it was cold and and I was underdressed - just making it to the halftime show was no easy feat. Before the band took the stage, they could be seen jumping around at the side trying to get warm for their performance. 

When they were finally given the green light that the broadcast was live, they fired through four songs while flames shot up from behind the stage and fireworks were launched at key moments - it was an awesome show, it's too bad it was only 15 minutes!