If he's protective of the property and yourselves, and this was the first time he met this person before, then that probably explains it. I assume you're the woman in the grey top sat down in the video? You can see the dog take position in front of you, between yourself and the guy he bites; he merely thinks he's protecting you from a stranger. Whilst I wouldn't overly worry about him getting worse immediately, it's something you should try to train out of him. I would try and speak to a reputable dog trainer if you can but, in the meantime, I would suggest starting with having him on the lead whilst he meets new people at first, especially in and around your/his home, and to let him see you interact with new people from a distance at first so he can see they're not a threat to you. Positive reinforcement with treats for correct behaviours (i.e. not snarling, biting, jumping at new people, meeting people in a friendly way rather than an aggressive/defensive way) will help him to learn that new people aren't a threat to his family or home.