I've called the EVgo hotline before (to report a problem, not to ask about policy) ... I wonder what they would say if you asked them.
Here's the thing about EVgo though ... it kills the charging session after 45 minutes and you have to manually restart if you want to keep charging. I have been in a situation before where I did restart because I needed >80% and so my total time at the charger was more than an hour.
So probably for a lot of the time between your 10am arrival and 11:40 departure his car wasn't charging. Which makes it worse and I totally understand your EVED.
As for the disconnecting a cable on an offending car .. I doubt any manufacturer allows disconnecting without unlocking by someone with a key. Maybe others here will know for sure.