From the article:
"Coronal holes are believed to form in areas where magnetic field lines emerge from the sun's surface but do not loop back there. This causes open field lines that spread to fill the space around the sun."
What they really mean is that the field lines extend infinitely far into space before they return. Along this line, the field lines are parallel and extend to infinity. This allows charged particles to escape since charged particles cannot cross field lines without expending energy.
This is a common error, often made by reputable sources.
Magnetic field lines cannot be broken. They are not physical entities, they are simply indicating the direction to the pole. All field lines are closed loops. There is no such thing as a broken field line because you can't have an end. It would be like having a spot on the Earth's surface where the direction to the North Pole was undefined.