Welcome. Not strange really ... installing a plugin via Moodle Admin is a process of steps ... one is to check the type of plugin (everything in moodle is a plugin), another to check compatibility with core version, etc.
Plus there are diff's in Linux (standards based apache/web services) and Windows IIS.
Plus Plesk itself ... compared to cPanel/other panels it appears to me to be on the paranoid side ... which is ok for a WordPress or a Joomla CMS, but can affect moodle (location of moodledata) adversely.
But ... mission accomplished ... so no sweat the 'small stuff', right!
'SoS', Ken