>>28502865 (OP)Porsche at fault.
There's no rule to let faster cars pass, in fact the rule is to not pass at all.
BMW was following a line, even if it was a garbage line, out in out for that first slight left and he was setting up to do it again at the next slight left.
RHD BMW so the porsche is in the blind spot the entire time.
Tries to floor it and sneak through without a clear signal BMW is letting him pass (everyone indicates for this).