Google-drive – Google drive shared with non Google account

I suggest checking and disabling any and all sharing for the Sheet in Google Drive. That should stop anyone who has the link from using it or sharing it (accidentally or purposefully) and further

I think that the answer is most likely "no".

Your administrator has said that you cannot use Docs/Drive, so when you are logged in with your institutional account, you are simply not going to be able to access a file that's in Docs/Drive.

Now, yes, a Docs/Drive user can share a file with " a Yahoo email" - but that' only because it is possible to have an Google account whose account-name is a text-string that just happens to look like a Yahoo email address. When that person tries to access the file, the first thing they are asked to do is log in to Docs to look at the file which has been shared with them.

(I just tested this: when I shared a .doc to a Yahoo address that is not associated with a Google account, the Yahoo email got the emailed invitation to view the document, complete with link. But the first thing that account was asked to do was log into Google in order to view the file.)

Bottom line - the person who is sharing the file with your institutional account needs to be told that you cannot use Docs, and that the only way to share a file with you is to either share it to your personal account, or email it to your institutional one.