I'd be willing to bet that your tortoise is of a Mediterranean variety, no? I've seen little Greeks on YouTube chasing cats and dogs. Seems pretty much what they do. First time I saw it I was thinking the tortoise was mad at having another creature in its territory, but as I started seeing it more often, I thought maybe it was a breeding thing? Who knows. I wish we WOULD be able to see into those little pea-sized brains and no what goes on in there!
Ha! I was thinking Mediterranean as well. I've seen that video, that's one determined tortoise. My red-foots, sulcata, and box turtles will chase my cats when they walk through their pen. Tortoises are extremely curious and want to check everything out that's new to their environment.