Yeah, that claim definitely requires a bit of an explanation. Let me try and show you where I'm coming from with this.

Our current global economy is structured around growth, with many large feedback mechanisms in place to promote growth. Not all economies work that way.

The Romans, for example, were excellent at recognizing and adopting technology and ideas other civilizations had. However, just about the only actual invention they made was concrete. After Rome fell, there was a dark-age period where much of the knowledge that that the Romans had gathered was lost. Then there was a period of extremely slow growth as a few new agricultural practices were implemented and some of the lost classical knowledge was rediscovered due to the crusades. But if you were a landed baron, you would expect the same yield in rents and crops from your land each year, not a constant rise in productivity. Money changed hands, but there wasn't much in the way of economic growth.

Oddly enough, the thing that really kicked things off was the black death. It killed a third of Europe, and suddenly there was a massive labor shortage. Land was the primary unit of wealth, and there weren't enough people to work the land. This effectively made labor much more valuable, and made labor saving devices desirable. Before that, labor was so cheap that it just didn't make sense to use anything else. This led to a ton of inventions like the Gutenberg printing press, and to the spread of things like windmills, which had been invented long before but never saw much use while cheap labor was available. This oriented large chunks of society around science and technology, and arguably led to the institutions that brought about the enlightenment and industrial revolution. Perhaps several other factors besides the black death helped things along, but the plague had a huge impact, especially on the ~100 years directly after it.

I could easily see a society focus it's efforts purely on the near-term, with no long-term investments. Often, research into things like mathematics doesn't get put to practical use for hundreds of years. Is our current research into string theory going to help someone build a better car within our lifetimes, let alone within a business cycle timeframe?

The mechanisms of science are large, and expensive. They require many thousands of specialists with domain-specific knowledge to work full time on expanding human knowledge. Someone has to pay for all that, and I can easily picture a society structured in such a way that such funding isn't available. Then maybe you'll get a few rich eccentrics funding their own curiosity, but I don't know if that would be enough to kickstart a second scientific revolution.

This is especially true if we deplete our fossil fuel reserves. Our industrial revolution ran on coal and later oil, but I suspect that it would be much more difficult to kickstart such a massive movement using all-electric tech and renewable energy. Good solar panels and wind turbines do eventually produce more energy than it takes to manufacture them, but only because they are mass manufactured on an industrial scale. If I were to hack something together in a lab or garage, I would be surprised if I was even able to break even. This hints that the "activation energy" threshold for kickstarting a technology oriented society may be much higher if we deplete our oil reserves.

To make things worse, society may not WANT to recover. If we almost destroy ourselves with technology, I find it likely that many people will be against technology in general. I suspect nuclear weapons and the cold war were a large reason for so many hippies rejecting technology entirely. And honestly, I can't blame them. It's better to be alive without tech than dead with it. But if such sentiment became widespread and entrenched in everyone's consciousness, it is unlikely that any government would ever fund the sciences in any way remotely like how we do today. Perhaps they'd have military tech research with very short timescales for innovation, but no long-reaching research into science which wouldn't find practical applications for generations.

All that being said, I don't think the default result of any economic collapse or civilization decline is going back to the stone age. It's probably well below 50% probability, maybe even below 10%. But I highly doubt it is justifiable to put it below ~1%. It's possible that a massive disaster might actually have the opposite effect, like what the black death did. But if the global science budget is what's cut when budgets get tight, then I would expect an eventual decline in the rate of technological progress.