Not exactly. They were afraid the government would use a standing army to enforce its will on the people. And it has been used in that way before, just as predicted, though perhaps not as frighteningly as in China. But it's also worth pointing out that a standing police force with paramilitary training fills the role the founders feared of the military.
In other words, if you want to know exactly what the founders feared, look at no-knock and warrantless searches, asset forfeitures, brutality in prisons, etc. Today, we don't even bat an eye when a cop calls non-police "civilians". There was a time when that was seen as a very disturbing trend...
With SWAT teams and the like, it really is amazing just how much force the state could theoretically use against its citizens. One could argue that great force is necessary to combat new threats like terrorists. But even if so, we need to think carefully about how we use this massive police power we have.