alfred,
EJBs are not your typical
java inheritance objects. The app server are not performing
polymorphism on the remote interface to the
ejb object implementation. In fact as you stated, the ejb does not implement the remote interface, so they are in fact not related from an inheritance point of view.
Now, i dont know if its in the J2EE spec, but most J2EE App Servers will inspect your EJB during deploy time and enforce the rule that all the methods in your remote interface are implemented in your ejb class (and, as some one pointed out, make sure your dont throw RemoteExceptions). So during runtime, the J2EE App server will match the methods being called on the remote interface to the ejb. How it does this, I wouldnt know, there are many ways, one quick and dirty way would probably be using introspection.
Cheers