The "nine" and "seven" mentioned by Zheng Zeshi in this context are Cantonese homophonic swear words, referring to male genitals, and "one" is a quantifier. Ninety-one and seventy-one means having nothing, but it is described in derogatory and vulgar terms: He didn’t want to scare him a few years ago. Ninety-one and seventy-one, free translation in Mandarin: He didn’t expect that a few years ago he looked like a dick. Nothing left.
Because swear words cannot be used directly in movies and TV shows, the homophones of "nine" and "seven" are used.