Basically one of the Japanese guys dismounted badly, they didn't award him for the dismount at first but did afterwards, apparently it was right due to the experts. Hence the British went from Sliver to Bronze for a team not expected to make the final it was still a great achievement.
Of course the Express journalist (if they have any) probably know about as much as me about the event, I would personally go with that he fucked it up, but I bow to the experts who know this sport, let's face it if the other papers admit they have journalists following events they have little knowledge of then the Express probably just pick opinions off twitter.
I believe that what happened was that initially the Japanese guy was judged to have fallen off the horse and marked down accordingly. The Japanese team appealed and pointed out that what actually happened was that the gymnast screwed up the dismount. This was accepted and the score adjusted accordingly. Obviously falling off loses you more points than a stumbling dismount. This was the difference that put the Japanese team into second place. As far as I'm aware the GB team and officials accepted the process and the final decision.