Qualifications for this response and advice ... a former joomoodle/joomla admin/user ...
Your discovery means you used another tool to view tables in moodle ... the mdl_user table.
Go back to viewing that table and you will note (or should note) user id 1 is guest and auth is manual. User ID 2, unless you changed, is 'admin' and auth is manual. Those two accounts in Moodle need to remain manual for reasons such as the snafu you are experiencing now.
It is hoped, you can navigate directly to the moodle site login screen and use the username/pass form in the left panel of that screen to login as 'admin'.
Advise you create another account in moodle and set it also to manual auth as well as site Admin.
*Never* change those. You have multiple accounts both in Joomla and in the Moodle to be able to test things Confusing for admin level users.
In looking over joomoodle's wiki I saw where in config of the plugin there are supposed to be 'test links'. One in Moodle and one in Joomla's admin panel.
Please see: https://www.joomdle.com/wiki/Main_Page
Comment: one of the reasons I got away from using .... updates/upgrades to either the Joomla or the Moodle would cause such issues as you are facing now ... and always at a very bad time. Learned to check both the wiki + plugins for Moodle for compatibility and/or issues prior to pulling the trigger on updating Moodle and/or Joomla. And a note about that ... me thinks security of Moodle perhaps a little better than Joomla ... one can get away with a Moodle less than latest/greatest where as in Joomla ... more like a 0 day flaw in Windows ... better get the updated version in Joomla. Nice thing about Joomla 3+... it's admin side has the ability to update the Joomla inside the joomla. Moodle has no tool for such but by far using git to do command line only updates/upgrades to the core Moodle code ... not the joomoodle addons, is the best way to go ... that's if one has access to ssh/shell and not afraid/adverse to a little command line 'foo'.
Best of luck!
'SoS', Ken