That's partly correct. People in Mumbai are generally more pre-occupied with themselves and won't offer to help a stranger (or for that matter, a friend), even if you are limping or hurt. However, we also saw how they went out of their way to help people stranded in the Mumbai floods in July 2005.
This does not necessarily mean that they are rude. I have found them to be very patient with their traffic jams, definitely much less abusive than Delhiites on the road, and much more well-behaved than Kolkattans on the road. They are less likely to pick a fight than a person from the north, for instance.
Possibly Mumbai has ended up bearing the brunt of a faulty methodology, designed by a Western mind for Western cities. This may be the reason why New York has fared so well.
And in any case, Delhi (or any other Indian city) was not included in the survey, so we have little to celebrate, except being happy at Mumbai's discomfiture.