If the event did actually occur, I'm curious about the order of battle (which divisions/generals were involved, for example). What were the Germans intentions in attacking the bridge, and why was the purported slaughter ultimately inconsequential?
Because of its proximity to the German border Nijmegen was one of the first cities to fall during Fall Gelb. The XXVI corps ( 18th Army ) was attacking in this sector and movements on Nijmegen started early in the morning of the 10th May and the bridge was blown up without getting crosses. The Waal was crossed elsewhere and the bridge itself wasn't crucial for any major movement. In general the advance during the Netherlands was fast and mostly without problems.
The Bridge over the Waal obviously had complelty different values in 1940 and in 1944. Germany in 1940 was already on both sides of the Rhine and the Waal runs from the east to the west. The Dutch defensive doctrine wasn't focused on fighting the Germans anyways most major bridges were prepared for destructions. Delaying the German advance was the main objective. Slowing the Wehrmacht and then repelling the attack with French forces.
In 1944 the Rhine and its side rivers were vital defensive lines for Germany and a crossing a major allied goal for several months of combat.