I don't think we will ever know why a chicken's personality changes suddenly. As humans, we can't know what goes on in those little pea brains.
I would not wait until he goes after you again to get him moving out of the way. I would suggest you go on the offensive and act first. That way - if he gets the message - he will always think twice about coming after you. Don't ever let that door open again. That's how I would handle it, anyway. Again, it's your bird and you need to decide what's the best course of action. If he's fine now, maybe give him time. If he comes at you again, then you spend the next few days on the offense, and hopefully reset his little brain. I hope it all works out for you so you can keep him.
I would not wait until he goes after you again to get him moving out of the way. I would suggest you go on the offensive and act first. That way - if he gets the message - he will always think twice about coming after you. Don't ever let that door open again. That's how I would handle it, anyway. Again, it's your bird and you need to decide what's the best course of action. If he's fine now, maybe give him time. If he comes at you again, then you spend the next few days on the offense, and hopefully reset his little brain. I hope it all works out for you so you can keep him.