Again the problem I have with this is the timing and perhaps the location of the University/College in relation to Inglewood. If there was an underground explosion of that sort of level that he could hear, then it is likely that the might have felt the ground move. To make cracks in the ground of that size it needs to be a reasonable major jolt.
An earthquake or explosion wasn't something that any of the reports they collected in
the Tower mentions. It seems to be likely that might have come up at some point.
Also, he left class and depending on how long it took to find a TV there were already reports from the news stations which would seem to fast to me.
On the other hand I have no other explanation for how this occurred at all. :)