The experiment showed that the CO2 gas was an efficient absorber of some form of radiant energy that came from the sun. We now know that this energy is infrared radiation. This radiation is emitted by hot bodies, and the sun emits a lot of it.
But yes, you are correct in that her experiment was not about the greenhouse effect itself - which includes more complicated interactions such as the reflection and emission of IR from the earth’s surface. But, still, the absorption of IR by CO2 is a very important component. And her observations - using the sun as the source of the infrared - is also a very relevant observation. This is because:
Infrared light can carry heat energy from one hot body to another
A large amount of the heat transfer from the sun to the earth comes in the form of infrared light
CO2, which is present in the atmosphere in a significant amount, is a strong absorber of infrared light
So I don’t think her work is irrelevant. It is very relevant. But I do think that the title “Scientists understood physics of climate change” is stretched because this experiment by itself is not enough to describe all of the complexity of the green house effect and climate change.