That's why I posted it, prairiebreeze. I do wonder if this is a next-morning rewrite, editing that out. However, I suspect the World report was prepared in part from local reporters who were there at the game. No way to know where that piece of information originated and how verified it is.
I know a number of people who were there at the game. I intend to ask them Monday morning if they heard a second explosion. I think a second device would have been detonated on-site, but am not sure.
One of the other posters on another OU fan forum (not the one where I post) said they heard the 2nd detonation, that it was muffled, but felt the same. He said it was "south of the South Oval" and heard it while he was walking to his car.