<human>: Can you give me the gist of the text in a nutshell?

I have a 3 1/2 year old cat who has never pooped outside his box except today, when he decided to take a crap in the middle of the basement floor. There are a lot of factors at play, but basically I'm wondering if 1) I should be concerned for his health or 2) if this is a new thing that he's going to keep doing.  

* Kitty is very fat, but not so much that he can't climb, run and play. He gets both wet and dry food.
* He lives with another cat - they have lived together for over a year and play fight, real fight and groom each other. Usually they're bros and we don't have a problem.
* My new room mate had 3 (very loud, kind of obnoxious) people over at the time of the incident, and my other room mate also had a (calm) house guest. My cat actually goes out of his way to be around groups of people, though. They were giving him lots of attention and hanging out in the basement, so maybe he got overwhelmed?
* The basement is where the food and litterbox is. Unless one of the guests locked him out of the bathroom, he was 3 feet from his litterbox.
* The box had just been cleaned at the time of the incident. 
* Someone saw him trying to "bury" the shit, which is why we know it was him.
* Generally, I have felt that he's a bit off lately. Could just be in my own head, but he's been less snugly and spends more time at the window stalking back and forth when he sees the neighborhood strays.
<bot>: My cat just pooped in the middle of the floor for no clear reason. Why? Will he do it again?