If you don't specify @Resource's lookup attribute then WildFly will always provide you with the default instance, no matter which value you define for the name attribute. Which ManagedExecutorService instance is the default is configured in the same EE subsystem, by specifying the instance's JNDI name:
<default-bindings context-service="java:jboss/ee/concurrency/context/default" datasource="java:jboss/datasources/ExampleDS" jms-connection-factory="java:jboss/DefaultJMSConnectionFactory" managed-executor-service="java:jboss/ee/concurrency/executor/default" managed-scheduled-executor-service="java:jboss/ee/concurrency/scheduler/default" managed-thread-factory="java:jboss/ee/concurrency/factory/default"/>
Yes, it's pointing to the instance you mentioned in your post, that's the default ManagedExecutorService.
I wrote a blog post when JSR 236 support was introduced in WildFly 8.0.0.Beta1, and nothing has changed so far with respect to the configuration: