My understanding of it is that the distinction between 'dangerous' and 'careless' hinges on whether collision or injury could be a reasonably expected outcome of the driving. If, for instance, I decide to stop on the motorway and reverse back to the junction that I've just driven past, that would probably be dangerous. If I crash while distracted by changing the station on the radio, that would probably be carelessness.
I suppose what the Fiscal has to do is take account of both the action and the consequences and, in some respects, in terms of assessing the action they need to, for a minute, disregard the consequences in determining whether the driving was careless or dangerous. Before the incident (whatever resulted from it) was the driver being careless or dangerous?
Of course, we don't need to agree with the charge but I haven't seen anything that explains what the driver was doing in this incident.