Maybe we are not watching the same vid but isn't driver A the black hatchback (XFG) and driver B the sedan (XRG)?
If this is the case, XFG's bumper was infront of the XRG, however the entry to the chicane is a left.
So, XFG on the right, overtaking by a tad.
XRG on the inside.
IMO, XFG, while only having a bit overtake, took the chance to cut into the XRG bumping him just a bit.
Lag took care of the rest.
While some might call lag accidents like this "racing accident" ot no fault, we are all fully aware of the contact issues and as such, this IMO is A's fault.
Agreed, B could have layed off a bit and let him trough but what are the chances of that happening on a pub server?