You may be right, Becca, that this cat does have a really loud purr, but I don't think what we're hearing in that short video clip is really a purr. Purring generally is a more continuous sound & vibration, not just a rather short burst of it.

PBS has aired a special on cats a number of times, and I think that's where I heard about the findings of research on cat sounds analysis that showed that they "say" a lot more than just "meow." They have quite a few different utterances, which seem to have different "meanings," and some of them sound very much like what this kitty is "saying" in the video clip linked to above -- only not a loud.

I once had a cat whom I named "Murphy Prang," because he could, and often did, basically "say" his own name. Much like Smokey in the aforementioned video, he would say, "Mmrrrrphhhhh!" or "Prrrrrrrannnnggg" (or even "Mrrrrrphhhhh-prrrrrannnnnggg"). He could, of course, purr too, but that was "cat talk," not purring.

If this cat truly has a very loud purr, I would love to hear a recording of it where the "purr" goes on for more than 3 or 4 seconds.