URL: https://translatewiki.net/wiki/MediaWiki:Savedrights/en
This message refers to userrights being saved. Actually user groups are being saved. So the message should say for consistency "The user groups of {{GENDER:$1|$1}} have been saved." Messages like "userrights-lookup-user", "userrights-changeable-col" and "userrights-editusergroup" on the very same special page already refer to user groups.
I am aware that this message dates back to the dark ages of MediaWiki so the name of the special page and the name of the log should probably not be touched.