Yes, I know what you mean there, and its a good point

It does not always help to confront and I would say if you hadnt seen your son for a long while, I wouldnt worry.
One thing I learnt was ITS NOT ABOUT BEING RIGHT, ITS ABOUT BEING EFFECTIVE
I think that is a helpful rule.
So, when my dd took an OD, she was in hospital saying she didnt, I knew she did, but I thought, what was the point in trying to be right? would it help the situation? No, I just wanted to validate how she felt. I decided to leave it.
Im not saying thats always the right way to do it.
I have a different problem, its when I say she has got BPD, she says, you dont think I still have that do you
Thats usually when she has been through remission or good times.
Anyway, you cant tell her, she does rigid thinking, she cant hear those truthful bits.
Also, another thing that will help you, get a copy of Valerie Porrs book if you dont have it already, read what she says on lies and BPD, very interesting and insightful.
Also, what I want to say, is well dont for seeing him again and being there for him, I hope it works out for the best in the end.
One last thing is that it was your first time seeing him in 4 years, build up your relationship first maybe may be better or you could loose it. He will be ultra sensitive, so it will hurt him much more than other people.