"Global cooling was a conjecture, especially during the 1970s, of imminent cooling of the Earth culminating in a period of extensive glaciation. Some press reports in the 1970s speculated about continued cooling; these did not accurately reflect the scientific literature of the time, which was generally more concerned with warming from an enhanced greenhouse effect."

I would describe it a sample of irrelevant pop science noise from the past, that AGW deniers like to mindlessly compare to the current well established theory of AGW.

“An international team of specialists has concluded from eight indexes of climate that there is no end in sight to the cooling trend of the last 30 years, at least in the Northern Hemisphere.” – New York Times, Jan. 5, 1978

Here we have the paper of record making some rather official pronouncements and claiming the weight of scientific authority in said pronouncements. That sounds like more than "irrelevant pop science noise" to me.

Now, hardly a month after that second quote, we also have this one:

“A poll of climate specialists in seven countries has found a consensus that there will be no catastrophic changes in the climate by the end of the century. But the specialists were almost equally divided on whether there would be a warming, a cooling or no change at all.” – New York Times, Feb. 18, 1978

Which is a fairly significant change in position that should not go unnoticed, but it does nonetheless leave me somewhat skeptical of Wikipedia's claim (I'm still reading the source of that claim).

But even if the reporting on the state of climate science in the 1970s was wrong: why was it wrong? And what has changed to fix it?

Well, because this was a thing in the 70's, so before you were born. I remember the headlines in pop-sci magazines were screaming about "the coming ice age" and artists depictions of glaciers in New York, Chicago, etc.

It doesn't invalidate the current climate science, but plenty of people remember that old sensationalism.