I wouldn't worry either. Our Rosie turned 2 in August. 2 weeks ago my husband had to go away on business so that left me walking her after 10 PM. I was so tired and after 10 minutes she wouldn't poop even though I knew she had to go. I called it a night knowing there was a possibility I would wake up to find poop in the kitchen and sure enough I did.
I did not get upset knowing that it was my fault.