Tomato or cactus fruit?

These pictures are from November, I never got around to doing anything with them. The cactus growing to the right of the garage door at work seemed to be fruiting (is that even a term). When I first saw it though I thought someone had shoved a tomato on the cactus.

That isn't as bizarre as it may seem. We have 2 tortoises that roam the front and back yards at work and we just lay out greens and other things for them to eat. The dogs LOVE to eat the greens. I've never met dogs that love greens, fruit, and vegetables as much as them, and all three of them eat the stuff.

What I thought happened was the tortoises ignored the tomato and to keep the dogs from eating the tomato and to be able give the tomato back to the tortoise at a later point it was placed on the cactus. As the day went a long I decided to take a closer look and get a picture of the tomato on a cactus and when I got closer I realized that it was actually a cactus fruit.

But still looking at it as close as I could get with out getting poked I was not convinced it was actually a part of the cactus and not something stuck on it. This cactus has been here for years and I've never seen anything like this on it. It's just so interesting to me.