If the user used <Actions>... <Connect to Outlook> to "subscribe", then
that user is actually deleting items in the list itself, which is why
users would receive alerts about items being deleted.
If the user used <Actions>...<View RSS Feed>, then, yes, they are only
viewing a copy of the sharepoint list.
So, it sounds like in this situation, the user possibly connected the
sharepoint list to his Outlook.