>I remember the UK government investigation into Huawei concluding that not only was their security posture insufficient for critical infrastructure, but their engineering practices were likely a decade away from being at a point where they could start to claim good security practice. This paragraph seems to suggest a similar problem at Xiaomi.

ASFAIK, Xiaomi does not sell any critical infrastructure equipment, nor is it installed anywhere; not entirely sure why GCHQ or NCSC would be involved, especially when there is ambiguity around which/what equipment they should be conducting a code review upon?

With regard to Huawei, there was no decisive conclusion, despite a comprehensive security review. Furthermore, it has been business as usual for currently installed equipment. All future decisions will be based around the 5G infrastructure.