Why Did Our Dog Poop On Top Of Stairs?

Our dog pooped after I left for only a half hour last night. He did it in the spot that usually waits for any one of us to come home. He is nine years old now, and is trained to do it in a designated spot in the kitchen. Now all of a sudden he did this. He isn't left home alone all that often. There is almost always one of us here with him. He has never showed any signs of separation anxiety. He didn't do any of the panting, no chewing or destruction, etc. Could this just be plain anxiety? Yes, he is a very dependent dog. He's a bichon and as many of you probably know they are a very clingy breed.