Hello Dinesh,
Lindenbergia muraria is not endemic. It's broadly distributed, rather you will find it in Flora of China too.
Guess by "exclusively on the walls of Bassein fort" Sweedle meant that in that particular area it grows on the walls of the fort.
Cheers,
-Swapna
--
Dr. Swapna Prabhu
Systematic Botanist/ Taxonomist
Bombay Natural History Society
Hornbil House, Shahid Bhagat Singh Marg
Dr. Salim Ali Chawk
Mumbai - 400 001.
India.