From the about page:
https://developers.google.com/speed/docs/insights/about
"Speed Score: PageSpeed Insights incorporates data from the Chrome User Experience Report (CrUX) to display real-world performance data about a page. "
"Optimization Score: PageSpeed Insights evaluates how well a page follows common performance best practices and computes a score from 0-100 that estimates its performance headroom. It evaluates if a page can improve its performance in two areas:
- time to above-the-fold load: Elapsed time from the moment a user requests a new page to the moment the above-the-fold content is rendered by the browser.
- time to full page load: Elapsed time from the moment a user requests a new page to the moment the page is fully rendered by the browser."
In this case, I believe PSI is saying "your page already is fast" (in the top 33%, based on real-world data, which may be good enough for your clients).
There are opportunities for improvement, although as the tool notes, further optimization is probably not necessary unless you're trying to be even faster than the page already is.