If we believed ChatGPT was the cause of an SO decline, then I'd expect it to also cause a decline in Google searches for programming queries. Here's the Google Trends data for two super-common error codes and one more conceptual programming search query:
https://trends.google.com/trends/explore?date=today%205-y&q=...
Maybe a little something going on with typeerror? Or just noise. But it definitely doesn't look to me like evidence supporting the article's claim.