It is worth noting that the Cambrian also coincided with the Earth releasing from an ice age that makes everything since look mild, as well as the increase of atmospheric oxygen to levels within an order of magnitude or two of today.

It is also worth noting that there is equivocal evidence of multicellular life before the Cambrian that nobody quite agrees on what it means - things that look like worm-trails in seafloor sediment a billion years old (but that some think could be trails from the motion of giant protists), flat sheets with a distinct center and edge 2 gigayears old, and macroscopic curly fibers two or more gigayears old...