The answer to the question in the title is that the scientist trained mother cats to eat bananas (for one minute put aside the morality and ethics of this experiment). He found that when the kittens were offered a choice between a meal of familiar meat pellets and a meal of the unfamiliar banana, most of the kittens imitated their mother and ate the banana. They had watched their mother eat bananas and copied her.
This experiment supports the view that watching the mother or another cat kill a rat or any other prey is enough to teach a kitten how to deal with live prey. It is not essential for a kitten to develop and hone predatory skills through hands-on play. Cats can become good predators via a variety of different experiences. There are many factors which contribute to a kitten developing the necessary skills to become a good predator.
Kittens learn by observation and this is facilitated if the cat performing “the demonstration” is known by the observing kitten. I presume therefore that it is normally beneficial if the kitten learns by watching mother or a relative of the family. It suppose they are considered more trustworthy than unrelated cats.
The scientist referred to is W. Wyrwicka. His work was published in 1978 and is entitled “Imitation of mother’s inappropriate food preference in weanling kittens”. The study was published in Pavlovian J. Biol Sci.