They did not fall simultaneously. In fact, the north side didn't collapse until a full quarter-minute (15 seconds) after the south end started falling. This is shown clearly on a surveillance video of the collapsw (looking toward the north shore).
The center section let loose on one end and I assume the weight caused the other end to let go quickly. The other sections of the non redundant bridge fall back towards shore due to no center span holding them together a little bit later. This was one of the last non redundant bridges built with this design (thank goodness).
I think he meant both sides of the roadway, not both ends of the bridge. It did look like both sides failed at the same time, the bridge didn't seem to twist much as it fell.
From the video I saw, it appeared that both ends of the span collapsed at the same time - no slow motion - and immediate.