Bitcoin is not the only project using POW so far, but the only thing the government is targeting is bitcoin, it shows that they know they can't control it, and they don't want to see it grow to threaten their power, not because POW is a waste of energy and a major cause of global warming.
Interestingly enough a couple of years ago the Chinese government released a list containing a handful of cryptocurrencies which they referred to as "trusted" and basically good cryptocurrencies. In that list you couldn't see bitcoin but you saw ethereum on top of the list!