It said that connections are often established quicker through HTTP/2 so you can likely expect metrics and the performance score to improve, adding:
In general, performance scores across all PageSpeed Insights runs went up by a few points.
If your page doesn’t support HTTP/2, you’ll see an audit which estimates performance improvements you could expect if HTTP/2 were supported.
So, if you’re seeing better scores and metrics in PageSpeed Insights for your pages, this is probably why.
Googlebot started using HTTP/2 last November to crawl a small number of sites. At the time, Google confirmed there is no ranking benefit to HTTP/2 and said they would only switch over sites that support HTTP/2 and which would clearly benefit from this.
You can check if your site supports HTTP/2 via this online tool.