You are speaking from ignorance.
The article in this case is not particularly clear, but the traders in this case were essentially causing a *broker* to modify their price using fraudulent bidding.
This was not some clever day trader beating the HFT firms on the open market using a clever hack. This was a group of individuals tricking their broker in to offering them the wrong prices.
The fact is that the actions the human traders took could be considered similar to calling up a broker, lying about how much money you have, and placing a fake order to manipulate pricing, then calling on the other line, and exploiting this price change. Or it could be considered similar to tricking a poorly programmed ATM to give you too much money. There was an *intent to defraud* IB by the traders. Norwegian law happened to recognize this strongly enough to convict.
In America, they would have gotten away with it, IB would have fixed the error, and we would have moved on, but this is only because of the lack of regulation of finance in America.