How does File permission work on mount point?

Question

An application in my docker container saves data to the directory /var/mydata and mount to the host location directory /var/data.

1. In my container, Only the root has permission to read and write into this directory /var/mydata. So the Host system's root will have the same permission?

   If yes, So inside my container I go manually by exec and change permission to chown -R 1000:1000 /var/mydata. What will happen because 1000 is john in the container and 1000 is adam in the host system.

now it is showing jhon is owner of these file in container and adam is the owner of these file in host system. So jhon and adam are same user ?

Thanks in advance.