As a Cantonese speaker, I love the effort here! However, the above isn't correct. This is an example of vernacular vs. literary pronunciation, and 請 has both pronunciations, depending on context. For instance, 請 is ceng2 when used as the verb "to invite", but cing2 in compounds like jiu1 cing2 邀請.
It shouldn't be conflated with the phenomenon later in that same paragraph about 懶音 "lazy pronunciation".