The main difference is that the Chinese government restricts or blocks several types of transactions, western central banks try to influence the market using specific policies, so it depends on what you define as "intervention", but in general terms Chinese currency do float freely but the government has more power to change its value artificially, for example, there's no "official" price of the US Dollar or the Euro, the Fed doesn't decrees a price for its currency, it can't do that because firms in the US are independent from the central government, on the other hand the Chinese government can set whatever official price they want and since it has almost complete control over the bigger firms it can force the market to accept it at least as a reference price, they have used that power in the past to keep their currency low and keep Chinese exports as competitive as possible