[netvarun]

I am also specifically interested in what techniques they they are using to determine the levels of change - Is it based on content changes or changes in (x)html tree structure?

[ashah]

since it says visual ping, perhaps render html => image and take diffs periodically , setting threshold to size of difference?

[matmann2001]

Since, you can specify a specific slice of the page to monitor, it's likely diffing screenshots.