My thought is that the aircraft on the taxiway became the focal issue for the Air Canada guys. Perplexed by what they were seeing* they probably plodded on not really wondering why the VARSIs were WAY over there and other lighting seemed so vague.
That is the very nature of becoming fixated.
However, the very fact they were seeing the taxiing aircraft hopefully means they'd never have simply descended into them.
*When Tower said they had 28R to themselves, you could hear the continuing hint of bewilderment in the reply.