Is it mental illnes or an act
If you come face to facae with him, try to be nice, but make it clear to him that you don't like certain behaviour if he starts behaving strange. After all he is a human being like all of us and his own behaviour might cause him distress too and probably he is ashamed of it the better he gets. Don't forget that he is not in total control of his thoughts and actions and he is vulnerable, just as we all are.
He may be getting better or his parents just may think he is getting better because he is being treated. People see what they want to. They love their son and want him to get better. Has he just started contacting you? If this is a change, he may have been severely depressed before and now that is resolving and he wants to reach out. In my opinion, w/o someone responsible watching someone when he is on medication, it is very hard for the doctor to get the right medication and dosage.
It doesn't sound as if it is an act, but he apparently is not confrontation so does go home when you ask him to.
My advise is, if he bothers you further and it starts to get even weirder, then tell his parents that you will get a restraining order. That may sound harsh, but maybe that is what the parents need to hear to watch him better and be in closer contact with the doctor.
There's a thin line. I think the problem here is the parents. They bail him out and excuse his behavior every time. He's not responsible of his own acts not necesarily because he's incapable of but more so because he doesn't have the need to. He needs to be submited to an extensive study to nearly understand what the problem is, but that is not your job. You need to protect yourself somehow. I think you need to report the incident.
My guess is that they have not identified the traumatic event that put him in this state. The meds just put the trauma off for awile.
keep your distance from him he shows attachments for those who sympathize with his problems and if you are not 100% stay away it's the best solution he'll move on to his next attachment
I think you should do what's best for you. If you think you can cope with seeing him - see him. If not - don't. I think he does have mental issues but I don't think there's much you can do. He's getting help so maybe you should wait till he's a bit more stable to see him. Do whatever you feel comfortable doing. Good luck ! x
Im not sure what it is. And it could be an act but then again it might not be. Ya never know with these type of people. Just be careful