Hi,

Encryption at rest is used for protecting your data from an unauthorized user who has no read permission in hdfs or has no access to cluster and is trying to read it from the disk directly. 

In your example the directory /tmp/user1zone1 has read access for all cluster users and hence user2 is allowed to read from it. 

drwxr-xr-x - user1 supergroup 0 2016-02-10 02:42 /tmp/user1zone1