I tell them China has multiple parties. What made them think it only has one? And what else did they say? Then we can go through the nonsense with a nit comb.

Edit: look at this shit: https://en.m.wikipedia.org/wiki/List_of_political_parties_in_China :

The People's Republic of China is a one-party state ruled by the Chinese Communist Party (CCP). Despite this, eight minor political parties subservient to the CCP exist.

Wikipedia calls it a one-party state in the same opening paragraph that admits the existence of eight other parties. What's the criterion for being a one-party state? That only one party rules at a time? A lot of states fall into that category. Would the CPC allow another party to take control? Unlikely. But again, if that's the definition, then a lot of states fall into that category.