Yes, it is possible that they accidentally used the same description as a previous character. However, when you run into it happening multiple times in the same week it is doubtful that many people are doing this by accident. Even 1 in 10 of these things happening being by accident would be a high figure. What I'm saying is that "Oops you weren't cheating" is not given by them claiming that it was a past character description. That is taken by the assumption that the person is being truthful.

If it concerns you that you might do this accidentally, there are many ways to prevent it. Including being more organized with your own files or always writing a new one when you start a new character (this is what I opt to do).

Stealing other other peoples descriptions is stealing their intellectual property. While you might think of it as "minor", I doubt those who have their descriptions stolen feel the same way. Regardless of if they do or not, it is against the rules.