The observable Cambrian was originally almost all from one site - one snapshot in time - The Burgess Shale. We did not know what was before as there were precious few fossil sites. As more are discivered two things become clear.Listen, you can call the Cambrian a piece of time if you want. In reality it is a depth of ground. And at it's very lowest point, not at the top, after millions of years have pasted, but at it's lowest point, you find these fully formed life forms with no preceeding ancestor.
1. There is significant evolution during the Cambrian period, with the simplest forms earliest.
2. There is multi-cellular life before the snap-shot period and the Cambrian itself, right back into the Ediacaran.
None of this violates the concept of punctuated equilibrium, but it should remind you that this period of evolution it was not "sudden" except in the millions of year timelines used in geology and evolution. You keep acting like PE was "poof!" one day nothing and the next, a seabed teaming with life. Nobody has EVER suggested that.
You have also been told, before, that the few Ediacaran fossils we have are soft bodied. If the Cambrian was the time when creatures started to develop hard shells and skeletons, which preserve more easily, of course it would look like a sudden increase in the fossils!