Was listening to John Batchelor last night as I was dropping off to sleep. He was interviewing a science reporter and they were discussing this topic. Fascinating! Even though Proxima Centauri is a red star and the planet is much closer to it than our earth is to the sun, the red star is so cool that the “Goldilocks zone” is just right regardless. Also, that planet does not rotate (as I recall), so one side is perpetually facing the red star, while the other is facing away. The reporter speculated, obviously, that any plant life would be on the side facing its red sun.
Don’t remember how they knew that the planet doesn’t rotate (was falling asleep - sorry).
Humm, according to what I read the planet is inferred through observed light changes of the parent star, the planet itself has not been seen - so no one can say anything definite just speculate.
All they really know is that there is an object that passes the solar disk of PC which they assume to be a planet at a certain distance. Everything else after that is just speculation.