They test AFAIK under ideal smooth road conditions asconfirmed by the picture. On bumpy roads the 10 watts advantage might quickly disappear

10 watts per tire is an absolutely enormous amount given that the rolling resistance of the tire itself is only 10 watts in total. The BRR test also claims that "the drum is covered with diamond plate to simulate an average road" - it isn't completely smooth [1]. If you're riding on roads that are so bumpy that you really need super low pressures (e.g. significantly lower than the 60psi you can run on a 28mm GP5000) then rolling resistance isn't a high priority. But honestly very few actual roads are that bad.

[1] https://www.bicyclerollingresistance.com/the-test