No, truly; he didn’t mean to walk in on you. Do you know how difficult it is to be royalty? Of course you do — and worst of it, you have to deal with being a vampire too. Argenti does not understand this predicament, so when he walks in on you trying to appease your starvation by feasting on your own blood, he assumes the worst. Give him some time, he will not be afraid of you. He just needs to… come around.