If I remember correctly, these things have been around for years, in one form or another... (although, the Mr-T one is a great version)...
It seems to me, they are running a form of a proxy server, that will go grab the page (site?) and compare it quickly to a list of "keywords" it has stored. For example, with the Mr-T one, wherever it finds the word "car" it replaces it with the bit about the A-Team van...