https://www.wired.co.uk/article/netblocks-internet-shutdowns
The Wired did extensive reporting on them and their unethical practices and is worth a read.
Please be extremely careful with their reporting. They don't publish their data and it's a mystery on how they get access to it.
The Wired article definitely makes the case that Netblocks is shady and seems to suggest all sorts of malfeseance. But nowhere in there does the article allege that the graphs published by Netblocks are wrong.
Reachable IPv4 addresses? Traffic volume? Client side HTTP/TLS requests? DNS queries?
Do they take whatever data they get, aggregate everything into one giant field called "connectivity", and evaluate the stability of a connection based on that success rate?
We don't know.
Also, many people use https://api.webprobe.org/ which reports data too
Again, please read the article as it covers all this and much more and why Netblocks is a problematic organization in this space. It's a detailed article.