favorites does not appear out of nowhere, there must be a browser sync setting somewhere that is turned on or some app is doing it. In addition maybe you had different browser accounts before and dont have it now. or it could depend on what was transferred from the old computer. There is no way to really tell you what happened.
My wife has just got a new desktop with windows 10, I have a desktop with windows 7. Her first task with her new machine was to set up her favorites she added half a dozen or so but when she checked her drop down she had all mine as well. The computers are not linked and are not even in the same room although we do use the same router, both machines are wireless, How can this happen, surely it cannot be right, in our case it does not really matter, 'nothing to hide here' where would the privacy be if it were 2 individuals house sharing! Any thoughts anyone..