Methinks this is not about morality or (the lack of) compassion, but being more aware of your environment, i.e. mindfulness.
I would suggests the other people simply weren't consciously aware enough to notice, but would have gladly given up their seat if someone else pointed it out to them.
I remember reading another story where, they observed people being immersed in compassion or at least, being considerate. The experimenters then told the experimental subjects they needed to hurry to another building. Along the way, they passed someone who needed help in some way. Generally, even though the people were pumped, the ones who were told to hurry were more likely to ignore the person who needed help.
I don't think it is fruitful to try to scientifically evaluate morality. Morality from my own practice, naturally arises from awareness of [i]self[/i] as well as environment. What the professor said about meditation fostering perception of interconnectedness syncs up with my own experiences of this practice.
I would suggests the other people simply weren't consciously aware enough to notice, but would have gladly given up their seat if someone else pointed it out to them.