Dual login Windows and OSX on an Apple computer (not dual boot)
I suspect it was a dual boot set up. This can be done via refit and would show a screen like this

You then get taken to the Windows or OS X login - but for both of these you can make this auto login so the process does not stop here and you go in as a user. In OS X probably as the guest user and I think this can be done on windows as well