No. The previous owner does not have access to your account. Once the car is set as Sold, the previous owner will no longer have an account in Carandus.com associated to his/her vehicle registration.
The only trace of the previous owner you will have on your account will be the record of the accepted previous services using Carandus.com.
Note that when you register, you create a new username and a new password and the previous owner can only have access to it, if you provide him/her that kind of information.