Hi!
There has to be an option to disable the "Standard scale" check box when creating a new scale.
Under documentation it says:
"'Standard' scale is a scale which can be applied to every course in Moodle. Only those with site permissions such as administrators can make a new scale 'standard'. A regular teacher can only create a scale for their own course."
However there's no such option under permissions or site gradebook settings, so by default any teacher can make a standard scale as is seems to be a case in our Moodle 3.7.