There would be similarly named domains/servers/apps in a monitoring env (more so for jboss, oracleas and tomcat) that makes it hard to uniquely identify them in Core dashboard (Data-Tree view, Data-Management dashboard, data browser)
JEE-7617 filed for enhancement request
On the JBoss side, the name 'default' is the jboss server configuration file set. These can be changed manually and will reflect in the Core dashboard. (e.g. copy JBOSS_DIST/server/default to JBOSS_DIST/server/<hostname> and start JBoss by running the commadn run.bat -c <hostname>)
For more information, please see the following JBoss documentation.