I assume you're talking about Cranwell and an IOT graduation? And, presumably, the C130 dropped the Falcons parachute display team?
The low fly-by from the C130 is a legitimate part of that display, and all free-fall parachute displays are (by law) notam-ed. The display itself would have to have been arranged some considerable time in advance - Hercs don't bimble round with an itinerant free-fall display team on board, looking for an unsuspecting giding club to upset! I suspect that the truth is that your gliding club CFI hadn't received or seen the appropriate notams, not that they didn't exist. As for the DC3, I have no idea!