It's far too early to speculate, but from the reports I've seen, it could have been worse. No high-yield detonations, plenty of flash, smoke and concussion, but little shrapnel effect. Smells homemade to me.
Two dead are three too many, obviously, but it could have been 100 times as many, with that many people around.
Also, why did they wait so long to detonate? From what I've heard, the winner had crossed the finish line four hours before the blasts.
We are all dreams of the Giant Space Butterfly.