Earlier quoted context omitted.
Also, China was a Second World country (at least, back when the distinction still made sense). Of course, at some point, "Third World" became synonymous with "poor", and was euphemised to "developing".
When Mao created the notion of the Three Worlds, he included China in the Third World [1]. It was (ostensibly) unaligned, whereas Europe (and to an extent Japan) was aligned, making it Second World. He (via Deng) specifically called out the Third World as underdeveloped. [1] “Speech by Chairman of the Delegation of the People’s Republic of China, Teng Hsiao-Ping, at the Special Session of the U.N. General Assembly: A…
There's likely to be a better source available to someone wanting to spend the time to find it.