They're not "requiring banks to adopt crypto" per se, at least the formulation is misleading. The regulator is reminding banks that they have to accept legal customers, and can't cite "crypto" as a reason not to accept them. I.e., it's doing the opposite the US is doing, which just made non-engagement with the space a prerequisite for whoever will take over Silicon Valley Bank.

While the Beijing regulators do steer Hong Kong, it's still under One Country, Two Systems. Hong Kong is used as a laboratory to experiment while keeping the larger Chinese banking system (more or less) isolated. So this is the national regulator directing the local banks to prevent them from letting local risk-management or regulatory fears drive them to pre-emptively reject crypto companies.

I don't think this has anything to do with the digital yuan, or the BRICS interchange currency that's only in its pre-planning stage in any case. I'd assume, rather, that they're trying to profit from an increasingly negative US regulatory environment, trying to draw business to Hong Kong that otherwise would have moved from the US to Singapore or Malta. This seems the more likely direct incentive here.