HK/China Importing US Monetary Policy

With HK pegging the HKD (and China with the Yuan) to the USD, many say that they are effectively importing US monetary policy. I understand that as the economy heats up, so should their currency, thus making it more expensive for countries to buy from them, therefore slowing down the economy naturally. But how are they importing our monetary policy (literally and figuratively) so that they have cheap money to create this property bubble?

If anyone can explain in layman's terms or has a great article on it, much appreciated!

Thanks