China’s initial handling of the outbreak was sketchy for sure, however when it’s come to quarantine measures after that first few months, they have been a lot stricter than Europe. Chinese population is generally a lot more respectful of the prevention measures (they don’t really have antimaskers or anti-lockdown protests like in the West), and if they do, their government doesn’t hold back in disciplining that.
So yeah, a lot of Europe has enjoyed a lot more freedom, and this has inevitably resulted in more virus transmission and thus more mutations unfortunately.