This story comes from an English primary source from the twelfth century, what the Viking historian Gwen Jones (The Vikings, second edition) refers to as the "'C' Chronicle", which read as follows:

"The Norwegians fled from the English, but there was one Norwegian who stood firm against the English force, so that they could not cross the bridge nor clinch victory. An Englishman shot with an arrow, but to no avail, and another went under the bridge and stabbed him through the coat of mail. Then Harold, king of the English, crossed the bridge and his levies went forward with him; and there made great slaughter of both Norwegians and Flemings."

This may or may not have been folklore by the time it was reported. The article you cite takes liberties, as you can see, but much of the core information is present.