This isn't real science. Dr. Piff writes about all kinds of things at the Morality, Emotion, and Sociasl Hierarchy Lab. His latest work is on "Self-Transcendent Awe as a Moral Grounding of Wisdom", which sounds swell in a new agey kind of way, but it's not going to cure any diseases or launch any rockets. I don't know how a random person in public can be identified as to their income level without an extensive interview and research into their background, which I don't believe is done in any of these "experiments". It's all observation or casual conversation. They tried to judge people's income by the car they drove which is utter BS. The linked BBC article says this:

"Since Piff published his first batch of findings in 2010, other scientists around the world have been busy trying to replicate them. Some have found results which back up Piff's work, but others, confusingly have found the opposite.

One study in the Netherlands which used real-life millionaires as its participants found they were more generous than the average person when given a small sum of money to keep or share."

Analyses of population data by academics in Europe failed to find any link between wealth and a lack of generosity. If anything, they found the reverse, that wealthier individuals were more likely to offer time and money to others."