Move Along. Nothing to See Here.
I looked through the linked article - really just an abstract. If I understand it correctly, it indicates that an unpredictable event will interfere with the performance of an ongoing task. The analogy drawn to using a HUD while driving would seem to be that if something odd or different happens on the road while you are driving, you will most likely be distracted from paying attention to your instrument panel. So far, this seems to be good basic science followed by an odd inference: that a HUD (the primary task) might distract from something out of the ordinary on the road (the secondary task) and not the other way around. Perhaps I am interpreting the article incorrectly, but it is fairly well documented that we really have a fairly narrow amount of bandwidth to use when we focus our attention. If there is something odd going on when we are driving, we are likely to be distracted by it, both for good (e.g. another vehicle swerving near us) and for bad (e.g. a police stop on the opposite side of a divided highway).