I would think that is not very hard to accomplish. Their first flight is almost half a century after Concorde’s. Technology has progressed.

As an (imperfect) comparison, in subsonic flight (https://en.wikipedia.org/wiki/Fuel_economy_in_aircraft#Past):

“Jet airliners became 70% more fuel efficient between 1967 and 2007, 40% due to improvements in engine efficiency and 30% from airframes. Efficiency gains were larger early in the jet age than later, with a 55-67% gain from 1960 to 1980 and a 20-26% gain from 1980 to 2000. Average fuel burn of new aircraft fell 45% from 1968 to 2014, a compounded annual reduction 1.3% with variable reduction rate.”

Supersonic is different, but there was half a century of development in military supersonic flight, so a new design need not start where Concorde stopped.