Well, having now looked at the video, it is clear that the blue car on your left was in contravention, but for yourself, I'd say there was no contravention. You did not have to stop in the box due to the presence of stationary vehicles from what I see, as there was room beside the red car. You say you thought you had cleared the box, and the video shows you stopping partly in it then moving forward when you realised you were not all out of it so confirms your story. This is not an offence. Of course, inevitably, with the thousands of pounds the council well be earning from this YBJ, you'll have to take them to London Tribunals. This means risking the full PCN penalty, the discount option is not available there.
BTW you need to alter your view on what YBJs involve for the motorist or you'll get loads more PCNs.
1) At the point of entry no other stationary vehicle was inside the box on my path.
Any stationary vehicle on the
other side of the box that forces you to stop inside it, will get you a PCN too.