Each region must be associated with a continuum. On the other hand, each continuum may be (but does not have to be) associated with one or more regions. You can define multiple continua and assign a different one to each region.
The imported mesh was composed of one region, which was named subdomain-1. There is a simple way to determine which set of continua models are allocated to the region.
Select the subdomain-1 node in the Regions node.
Look at the Continuum property in the Properties window. It should be set to Physics 1, the name of the continuum where you defined all the models earlier.
By default, all imported mesh regions are allocated to Physics 1.
During this tutorial you will only see one continuum in the drop-down list above, but as you add more (to the Continua node in the simulation tree), they will be added to the drop-down list. This process determines which continua will be used in the analysis, though continua can be defined and left unused.