7T is the Nottingham University scanner. Cardiff is 3T Connectom A. These are different sites / scans in the article.

In fact, 3T Connectom A is actually more optimized for Diffusion MRI / white matter tract tracing compared to the available 7T scanners due to its enormous 300 mT/m gradient.

In theory, the best of both worlds would be a 7T+ scanner with ultra strong gradient system such as the one developed by the HCP team, but such device does not exist yet AFAIK.