First off do you know which shelter or rescue they got this kitten from? I would let them know the history of this person so they will be put on a no adopt list when this poor kitten goes missing too.
Next, sit down or email this person. Tell them all thaat can happen to a cat that is let outside. Inform them that when you adopt a indoor cat you have responsibilities to keep this cat happy. Cat trees, window seats, daily play activities, decent food, clean litter boxes and vet care.
If they turn a deaf ear, well theyve been told. May karma do a royal number on them. Then walk away from this friendship. They do not display the character you would want in people in your life. They are heartless and purposely ignorant cruel individuals