I thought Richard was going to yell out Dad!!
It seemed to me that when Mr C stepped off the elevator that he said: I'm here to see my friend, Rick not my friend, Ray as one might expect. I've watched this scene at least five times and it always sounds as if he is saying Rick (meaning Richard Horne his supposed son) not Ray. It's a minor point perhaps. All it would point to is that Mr C somehow already knew that Richard was there, that they may have some sort of psychic connection, which would further point to their being father and son.
I saw it that it was related to his meeting with Red. Perhaps it's a well known sanctuary if you're part of the drug running gang. Or perhaps Richard's friend at the police station knew someone there and got Richard in.
I don't think it's related to Mr C and Richard being father and son, other than if they are, it was a case of serendipity/fate them both being there.
If Richard is part of the gang as assumed by someone (correctly imo) he may have a relationship with Ray (Who said I know who you are). Richard possibly knows about his father. That look he gives at the screen isn't disinterested/worried as the other member's.
There's nothing quite like urinating out in the open air