And heard it over the background noise of a whole football stadium
Other than when something happens on the field, football stadiums are not all that noisy... from the outside. From the inside, it's a different story, but folks in there obviously heard the bomb detonate, at least some of them.
Sound, especially something like a gunshot or bomb blast, carries along way, depending of course on temperature, wind, humidity etc.
I used to be able to hear the hogs dropping the covers on their feeders on the next farm over from my wife's grandparents' farm, and that was about 1/2 mile away. Gunshots, even mere shotguns, could be heard at least a mile away.