Got a buddy Netflix. Can my buddy get access to my PS3 or my PSN account just because I'm logged in with his Netflix account? Or. Will my PSN account or my PS3 be linked to his Netflix account and what does that mean for me?
No.
No of course not. He can only see what you look at Netflix, add to your list, etc. Nothing outside of Netflix.
Ne. The only where I have a bit of control over a friend is Spotify, I have access to his account, because you can start playing on registered devices that are online and he has Alexa so that would theoretically always go that I play music with him. This is only because one can hear with a user only on one device. With Netflix you can look at 2 of the 3 subscription options with multiple devices at the same time, if he has the option where only one can look it could at most be stopped at one time because the other is watching, but really what is not working outside of Netflix
Can he see which PSN account I'm watching?
Ne. When you log in to your PS with Netflix, the Netflix account's email address gets an email telling you which device logged in and where. So for example:
"PS3 in DE, Berlin, IP address: … Signed in to Netflix with your account"
The PSN account is not mentioned (Incidentally, have Netflix and a PS3 & 4)