Rereading a couple times, I think the idea is that these heat waves are hotter than if the aerosols had never been released in the first place.

As less heat was reflected back into space over China, warming of coastal regions in Asia began, resulting in the development of high-pressure systems.

That, in turn, made low-pressure systems in the middle Pacific more intense, resulting in the Aleutian Low growing bigger and moving south which weakened the westerly winds that typically cool the sea surface.

The result was hotter conditions.

The meteorology is over my head but I think this is describing a rebound effect that caused more extreme weather.