That etyomology makes no sense. It is something I'M Lewis put together if i am not mistaken by using one Arabic word and a persian title. Combine two words from two seperate languages that don't fit with eachother lool and i think it was his attempt to validate the ''
Shirazi'' myths.
But persian founding claims have been pretty much rejected by modern scholars from what i've read , on several grounds , lack of archeological evidence, rarity of persian speech and costums etc, lack of documentary evidence of shia Islam in the muslim literature and so on.