Meiling and Meilan weren't necessarily good friends just because they came from the same elephant camp; making friends among elephants depends on personality and is more complex than with humans, and their feelings are even purer.
It just so happened that these two got along well.
If they liked each other, they would often stay together, walk and wander around together, and eat together. If not, they would display aggression when together.
For instance, when in the back shed, Meiling and Meilan liked to sleep huddled against each other, while Pingping preferred lying near Bobo.
When Pingping approached, Bobo extended his trunk first, touching Pingping's trunk, then raised his trunk and stroked Pingping's head back and forth, like an adult patting a child's head, signaling friendliness.
Pingping also touched trunks with Bobo, flapping her ears, and seemed very happy, opening her mouth and emitting a series of low rumbles.