Most investors are not actually qualified to invest in technology startups based on evaluating their technology. They rely on other methods, like investing in companies once they've already achieved some traction, or companies founded by well connected people, or people good at schmoozing.
It's a small flock of sheep all watching each other's moves because no one knows what they're doing. If the economic problems in China scare a few of the sheep, the whole flock will react.
The traditional style investors will freak out, but the people trying to scale startups (like YC) will just double down by investing in every good startup they see.