Bill, it is quite possible that no one cheated you, at least not intentionally. With an open system like the Google spreadsheet, the system has to be able to handle multiple changes from multiple users. I will attempt to do a simple explanation of what can happen using mostly fictitious people.
Bill opens the spreadsheet and scrolls to the bottom. The last name that he sees on the list is George. So, while Bill is looking things over, Mike logs in and opens a copy of the spreadsheet also. Mike also sees the last name on the list is George, and adds his name below George's. Mike's changes do not automatically appear on Bill's screen. He needs to refresh it to see the latest changes. Not being aware of this, Bill finishes looking around and finally adds his name to the bottom of the list, not knowing that Mike's name is there also. Google spreadsheet has to handle both additions but cannot automatically 'push' the latest change out to Bill's computer, so Bill adds his name below George and closes the spreadsheet and life is good, or so he thinks.
Google spreadsheet added the first name (Mike's) to the spreadsheet directly under George's , because it was added first, before Bill's name was added. Since Bill's name was added after Mike's, Bill's name got added to the list under Mike's instead of George's. But, Bill never saw that because he never refreshed the page.
So, the next day, Bill opens the spreadsheet again and sees that Mike's name is added to the list under George's name, and Bill's name appears under Mike's. Naturally, he is upset because that is not what he saw when he added his name. It truly appears that somebody pulled a fast one, even though that may not be what happened.
Autonoz, you might want to consider limiting the number of people that can edit the spreadsheet to help avoid this problem in the future. The possibility exists for upwards of fifty different individuals to edit that list, and it could potentially (though not probable) happen where all or many of them could attempt to make changes to it at the same time. Just think of the mess that could make!