This is a very good question. The processing of maocha under the sun is rather like that of white tea, during which some degree of “fermentation” takes place. Therefore, a maocha is not a green tea. You can read more about this in the related Tea Guardian page: https://www.teaguardian.com/nature_of_tea/Puer_cooked_or_raw.html
A sun dried green tea requires certain criteria for it to maintain the status of being a green tea: little or no fermentation.
To do that, the producer has to work with a very hot sun and very thinly laid tealeaves. That said, I have not really witnessed this being done in any green tea production. All I have understood about sun-dried green tea is from the books and a tasting of it years ago. I do not belief any sun-drying for green tea is executed nowadays.
The exact process with which the chemical nature of tealeaves changes from a maocha to a matured puer is yet to be studied by the scientist, but yet it is empirically understood that this would not happen to a green tea but to a maocha. Some studies exist though and I have it presented in this article: https://www.teaguardian.com/health/Health_Shengcha_Puer&ShuPuer.html
