How Does This Happen?

I saw this article, about a woman who was buried, but wasn't actually dead.

Is that hard to find out if someone really is dead or not? I mean, I know people can make mistakes, or that sometimes people can come back, but sometimes those who work in this field need to be absolutely 100% sure that someone is truly dead, before burying them.

I hope that the woman is as ok as she can be, with all that she went through.