Probably a couple of reasons:

Firstly, it wasn't until 1972 that the Peoples Republic of China (PRoC) opened up relations with any non-Communist governments, when President Nixon managed to thaw relations between the US and China. So, Chinese officials attending the funeral of a former Western Prime Minister, especially one as fervently anti-Communist as Churchill, was probably a little dicey in 1965.

Secondly, during the Second World War the leader of the Chinese Republic (before it became Communist in 1949) was Generalissimo Chiang Kai-Shek, who alienated and opposed the Communist Party of China. Chiang Kai-Shek, because of his actions during the Sino-Japanese War, was well respected by governments in the West, particularly the US and Great Britain. In fact, here is a picture of President Roosevelt, Churchill, and Chiang Kai-Shek at the Cairo Conference in 1943.

So, back to my point, the idea of sending an official delegation to the funeral of a former Prime Minister, a staunch Anti-Communist, and supporter of the previous 'democratic' regime, wouldn't really have made much sense to China in 1965.

Edit: why was that comment removed? It sounded like a good explanation.

It sounding like a good explanation does not always mean that it was a good explanation.

Questions that are based entirely on conjecture or speculation or unsourced opinions will be removed. We have a minimum standard of quality for top-level comments.

This is an academic subreddit and as such follows academic standard. If you're looking for something less rigorous there are other history-related subreddits which do allow guesswork and unfounded speculation.

I hope that answers your question as to why the comment you're referring to was deleted, OP.