The idea wasn't Cixin's. E.g., https://www.researchgate.net/profile/Alan-Penny/publication/... refers to speculation as early as 1967 that it might not be a good idea to answer that particular phone.

Here's a later article from 2010: https://www.sciencedirect.com/science/article/abs/pii/S00945...

Perhaps because the concept's been knocking around for decades before it was published?