Nah, Chinaman was always meant as a slur. I remember people referring to a “Chinaman’s chance in Hell”
I'm still not sure I buy that it's a slur. The reference you make here refers to the high death rate of Chinese railway workers back in the 1800's. It was not meant as a slur, but as an alternative way of saying something like "your chances are slim to none." It was a fact of their life back then, not a racial slur.