I have another thought, do you think his uncle and aunt didnt know that anakin was vader, kenobi mat have let on that anakin had gone bad and he had killed him, thats why they didnt want him talking to him as they didnt want their nephew knowing that his dad had become the scourge of the jedi.
I feel kenobi had thought he had left anakin to die and until he passed into the force thats what he thought.