Is he an only cat? Sounds like he may have left the box in a hurry.

Dmitri used to leave me "messages" like this, long ago.

It turned out to be that his anal glands were plugged up. Once I got
that fixed (regular vet visits to get them expressed), he stopped the
communications.

Has Mico been scooting on the floor at all? That's another symptom,
though Dmitri started the poop on the pillow before I ever saw him
scoot. I thought it was a protest that his litter box wasn't clean
enough. Then I caught him scooting across the carpet, took him to the
vet expecting worms, and found out he had this anal gland thing.

If you're up to the task, you can google feline anal gland (or anal
sacs) and probably learn to express them yourself. Or at least do a
check to see if they're full. It was painful for him, so I never had
the heart to learn to do it myself. I took him to the vet on a regular
basis for that. (Cost was the office visit charge, plus about ten
dollars for the expression)

Groomers can also do it.

I don't know if this is Mico's problem, but it sounds exacly like
Dmitri used to do, including not covering his stuff. I always felt that
Dmitri was in such discomfort, this was the only way he could tell me
"Help me, please." Oh, the other thing was constipation, and that was
relieved with baby food peas (he loved them) and canned pumpkin added
to canned food (he got used to it). Are Mico's stools really hard?

Juls

I have 2 females, one 12 years old, and the other 6. They are both healthy
and we have absolutely no litterbox issues. I am very fortunate, I know. My
girls are very, very good about always using the box and only the box. I do,
however, from time to time, notice little pieces of poop on the floor
occasionally. And, I know what it is from, because I have had to deal with
the source first hand. Because they pass hair they have swallowed form
grooming themselves in their feces, sometimes it doesn't just cleanly plop
out when they visit the box.
I am sorry there is no good way to delicately discuss this, but I am trying.
I found out this is the problem because both of the cats have at different
times over the years seemed distressed after visiting the box, and when they
were giving attention to their rearend, I investigated and found some stuck
to them. You can easily see the hair in it. I simply used a piece of paper
towel to remove the offending bit of stuff and order was restored.
If your cat doesn't exhibit any other behavior changes, I would bet this is
the problem. Maybe a small bit clings to his bottom on occasion and falls off
as he walks away. With you finding this last bit near the box I bet that is
what happened.
Is he a long haired kitty? Even short haired kitties get hair balls because
they swallow hair when grooming. Does he have a problem with vomiting up
hairballs? This is just a fact of life that comes with cat ownership. Buy a
tube of hairball remedy and give it to him as per the directions on the tube.
Bathing your cat will help to cut down on the amount of hair that gets
swallowed, but mine ABSOLUTELY WILL NOT consider this option. So, the only
option I am left with besides hairball remedy is to brush them to try and
remove loose hair. This works--when they are in the mood to be brushed.......
Hope this info is helpful to you. I hope it is just a silly thing like this
and no health problem.