Google has already admitted that a small percentage of serps contain test results instead of normal results. You probably saw one of their tests.
I have over a decade of benchmark data and I know when I am receiving garbage traffic. These days I am seeing periods of hours of low converting traffic followed by periods of hours of very high converting traffic. There are many of us that have been experiencing this phenomena
AMEN! I've been seeing exactly this on my transactional pages for some time now.