I believe NC is a great idea.
He manipulated his way into your home both times.
first by saying he was depressed, could he come by to see your DS
That got him in the door. Game changer in his head.
second, by showing up the next day, unannounced, and getting the same welcome.
If he does text you (I am not recommending initiating contact), state your boundary:
It is not okay to show up at my home unannounced. Period. End of conversation.
Whatever you choose, I think you handled yourself well when you found him in your home with your DS. No drama, congrats!
Congratulations to your little man for such high marks! Good Job!