This is an old image, so GPT wasn’t around back then. The top result of a Google search is often a sample of a webpage - Google estimates which part of the article best answers your question. The next sentence of the article probably tells you about the counting-rings method, but it was either cropped out of the image or Google didn’t choose to include that part of the article in the sample.
I think Google is showing why it thinks the result is relevant to the search. For example, the search used the term "find out," so Google bolded "know" and "determine," which it believes to be related to the question.
I just drove through the Redwoods in California and really couldn't believe how many rings the largest trees had. To be honest, it's way more wood than I even needed.