domain mapped, still using internal subdirectory?

Yes.
For example, http://lcblog.lernerconsult.com/2014-delicious-desserts-and-breads-diabetes-healthy/ (the domain mapped page, ancient history reasons for the lousy domain name, but it shows an example) is edited from http://lcblog.unmapped-domain.com/wp-admin/edit.php

Okay, I’m not sure about the “mapped a domain to my subdirectory”, but since “the mapped domain works as intended” you got it right. For others reading this, you can’t use domain mapping with a CPanel-created actual subdirectory; it only works with a WordPress-managed “virtual subdirectory”. Said another way, if you were to FTP to where your WordPress is installed, you should Not see the subdirectory there.