He may be doing this because he is responding to the nasty messages that you sent him on Instagram.
Given that he made his Instagram public the next day, after you had sent him those nasty messages, it was most likely a calculated move.
It wasn’t initially a power game with him. The first date that he went on with you that lasted all day seemed genuine enough.
However, you may not have heard from him after that date because he may have not been entirely happy with the chemistry that you both shared.
Though you believe that you both shared great chemistry, there may have still been something missing to him that you just didn’t quite have.
That alone may have been the deal breaker. He may have thought to leave it at that and move on. However, now that you have sent him nasty messages on Instagram, the power game may have ignited in earnest.
As of now, neither one of you has the power. However, he hopes to be the one to possess it.
This would mean that he has the upper hand on you.
He is hoping to do that through suddenly going public with his Instagram and posting stories.
He may be hoping that he is able to make you jealous in the process. This would give him a greater sense of power and satisfaction.