Depends. In the Active Directory world, policies can be applied at the user or computer level. Not sure about Chrome OS, but computer level policies absolutely can effect other users. I bet if OP signed into a normal, non-Google Classroom/organization affiliated account after they reset the device, they wouldn't have found GoGuardian running. This seems like if you connected an arbitrary device to a Windows domain over say VPN, then got surprised when user level policies were applied to the profile created on the local machine resultant from the process of connecting a machine to a domain. This is very much by design of ChromeOS as other commenters point out.