Able to delete the VM through SSH on console

That is because in the video for the console you grant the service account the "Allow full access to to All Cloud APIs" under Identity and API access/Access Scopes. See console video at 7 mins in. In other words it is not because you used the console instead of the shell, it is because when you were setting up the instance via the console you took the extra step to grant the service account the required permissions. It is also explained at minute 16

please do you have an answer to this now and how was your exam?