The Host are the virtual-host defined in the standalone.xml and in the webapps (basically a group of aliases). Each webapp can have its own aliases resulting in a Host created per webapp, but normally that isn't the case...
The Node correspond to the 2 boxes you are running.
It looks like you have something wrong because you have 20 nodes and only 2 boxes :-(
There can be several reasons to have that:
1 -The advertise of mod_cluster reach 20 boxes that are in your lab.
2 - Something wrong in the CONFIG message creates more nodes than excepted.
To test that check the nodes and the CONFIG messages in error_log once the log level is debug.