The immigrants in the story are from Zhejiang, so they likely natively speak a Wu dialect that does indeed not have an /r/ sound:

https://en.wikipedia.org/wiki/Suzhou_dialect#Phonology

And even the sound we write "r" when romanizing Mandarin is pretty distant from an Arabic /r/ (ر).

https://en.wikipedia.org/wiki/Mandarin_Chinese#Initials