The Dane was battling Sergio Perez for seventh, when he out-braked himself in Turn 2. On rejoining the track however, he failed to drive to the left of the bollards per the request of the race director.
Even before crossing the finish line the Dane made his feeling clear having been told of the penalty. "If we wouldn't have a stupid idiotic steward, we would be eighth," he said over the team radio.
"That penalty could have meant disaster for us," Magnussen subsequently told Sky Sports. "It was such a harsh penalty, for nothing.
"I just don't think it's fair to give Norris that position and McLaren those points," he continued, "because he didn't deserve it.
"It's not like I made myself undeserving of that position," he insisted, "because I lost that position to Perez, we were fighting for P7 and I went over that piece of crap track and lost my position. I lost a lot of time, fought hard not to lose another position and I would have been way better off if I hadn't gone over the run-off.
"So I have already got a penalty and then they choose to give me another one. It's crap.
"I come into the run-off with a lot of speed and I'm thinking it's not a good idea to try and stop the car and turn it," he said of his thinking as the time of the incident, "I'm focused on just trying to keep the car in control, and get through this bollard thing... there's three bollards, safely.
"I come out, I've lost a position, I've lost a lot more time than I would have gained by just going behind him, and I've got dirt on my tyres so the whole next lap is also very slow. I've lost a whole lot of lap time going through there.
"They see it, and it is 100 per cent a grey situation, it's not black and white, and they choose to give me a penalty and I don't get it. It's like, why would you give me a penalty when I haven't won anything, in fact I've lost a whole lot?"
"Unfortunately, Romain was caught up in a crash on the first lap which ended his day, but obviously no penalties were given there, it's all good," said team boss, Guenther Steiner. "Kevin, at the end lost a position, then he was given a five second penalty, which I think was completely inappropriate.
"Anyway, we got two points for ninth place, that's better than nothing."