The COVID lab leak conspiracy theory was promoted by high level politicians and news outlets. The origin point is largely irrelevant as it could’ve happened anywhere. China’s response was much better at containing the virus than that of the US, which is why fewer people died per capita. Public opinion of China was majority favorable in 2018, so the argument that it’s just because they’re a competitor doesn’t hold water.
The steep drop in opinion that you see in those polls is only really explainable as, like I said, the product of a massively successful propaganda campaign, the reasons for which I stated, to distract from the horrible mishandling of COVID in the US and to justify defense spending.