The mortgage holder has the legal right to take title of the property if the conditions of the mortgage are not met. In addition to liens and mortgages, any legal agreement can be registered against the title of the property. When you buy the title, you are taking ownership of all the agreements registered against it. This is why you hire a reputable lawyer. Every property has legally defined boundaries.
Boundaries are precise and they are illustrated in a land survey.
When purchasing a home, the vendor should provide you with a registered survey. The survey should contain the stamp of a registered land surveyor. Thomas and Anne's survey should have told them that part of their driveway was located outside of the land boundary. This is known as an easement and is quite common. If you have a shared driveway, there is an easement involved.