Earlier quoted context omitted.
He had, shall we say, "protections" in place to prevent his page from being embedded. Daily Mail downloaded his source files, removed the protections, and then embedded their own iframe referencing the copied files with the protections removed. I'd say that counts as stealing.
This sort of thing happens all the time with images though. It just sounds worse and different because it is a fancy visualization rather than a .jpg or .gif.
The fact that copyright is violated on a regular basis does not make this case any more or less excusable.