[supriyo-biswas]

It is perfectly normal for an anycast network operator to have multiple sites from which they make BGP announcements (which is how anycast works in the first place), which gives them multiple vantage points for this sort of analysis.

Other CDN companies can do it too, it's just that they don't work on signalling their engineering focused organization.

[bandrami]

This was a while ago but I think it was Akamai that pioneered that. I remember how impressive it was in the early oughts though we take it for granted now.