I would recommend making 3 changes here. One in Moodle's Admin block and the other in Moodle Plugins.

Admin: I admit this one is a bit obsessive compulsive (even for me); however all of the other elements are plural and it does refer to the various authentication plugins. So,

1) I would recommend changing the element in the block to Authentications and the text for the URL to Manage authentications.
2) Similarly, on admin/plugins I would change it from Authentication methods to Authentications.

MDLSITE: In Moodle Plugins, both Authentication and Enrolment are listed under Users. This seems slightly inconsistent to me. I would expect all of the Plugin types to be listed as categories.

3) I would propose moving the Authentication category out from under the Users category and making it its own and renaming it Authentications.