sheet ownership transferred over without owner accepting request

Someone who I made admin of a sheet I created was able take ownership of this sheet without me accepting the request. This has happened before without even a request submitted to take ownership and I don’t understand how is this possible, did anybody experience this as well? The same admin was able to take ownership of multiple sheets (multiple owners) and move then to another work space. I'm not sure if this is bug or something that is allowable ( I believe it should not be allowed)  I want to know what are the conditions to be able to to do it, when I ask the person he said he is not sure how he did it, he just move them and they show he is the owner now. I have tried to test and see if I can do this myself and I was not able to repeat the scenario. We are both Smartsheet Sys Admin. Please help me understand this. Anyone?