Is the PageSpeed Insight display score got from the “Lab Data” or “Field Data”?
I've randomly tested a web link and got 64. However, the Lab Data and Field Data seems quite different. I think it's because the web page owner just modified it.
Is the score “64” reflecting the Lab Data or Field Data?
Short Answer
It is lab data score.
Longer Answer
The score you see there is the "lab data" score, it is the score for this synthetic test you just ran. It will change every time you run Page Speed Insights.
"Field Data" will not contribute towards your score in Page Speed Insights and is purely for diagnostics.
The "Field Data" is calculated over a rolling 30 days so is useful to see if there are issues that automated tests do not pick up, but useless if you have just done a major update to fix a site issue (for 30 days at least).
Additionally CLS in "Field Data" is calculated the whole time someone is on the site (until the "unload" event on a page), the PSI "Lab Data" is only calculated on the above the fold content. That is sometimes another reason for disparity between results.