Yes, those were fossils from the Cambrian period (period named after where the fossils from that time were first found).
PreCambrian fossils were even simpler (such as lacking appendages and a large variety of tissue types).
The significance of this period is that these are the first known examples of animal body plans. Since the first animal body plans were being evolved then, many were weird looking to us today and are considered evolution experiments. Many current body plans evolved from these.
Many are soft body fossils which are rare because they have to be rapidly buried before they are eaten or destroyed by the environment. The Burgess shale fossils (a different Cambrian fossil site) are thought to be the result of repeated rapid burials by fine grained underwater landslides from a neighboring slope. These unlikely to happen events combined with the age of the rocks, make these fossils very rare.