Here's the issue: Boris Johnson is simply wrong.
Furthermore, we're not sure it's a great model for a closer relationship between Britain and China.
Cho and Harry's "relationship" consists of her initially rejecting him for Cedric Diggory, them briefly coming together due to the shared trauma of Cedric's murder, before the relationship quickly falls apart, they stop speaking to each other for ages, and she starts dating other boys. They both end up in relationships with other people.
This doesn't sound like an ideal outcome, in geopolitical terms.