It is from ChatGPT, which consolidated from various resources, including learners experiences from LingQ and other forum posts.
You can also search on this forum for “word of reading” or “words read”. Depending on method used, sources and research the number and vary widely. I think there is no research on word of reading = x CEFR level, most research is on known word.
It gives me a milestone to shoot for instead learning blindly. For me, my milestone is 5-7 million words read, before I decide to consume just for pleasure or give up if I am still getting nowhere and move on to another language.
Below is from Claude, similar kind of result. It mentions some studies as well.
