Definately a reaction to a new person and could set you back miles, hopefully once the visitor has left he will gradually regain his confidence.
Some cats are permantly like this, my big Misa being one case.
He will run and hide if anyone comes into the house or the doorbell rings but as soon as they have left and he is sure he is back out of hiding again, he especially hates men because of the abuse he received when young.
Sasa just hides!