There are 2 sides to this story:
One side has been explained very well by others which is that a teacher should not ruin childrens imaginations and on that I can believe.
The other side of it is the definition of what a teacher is supposed to do, a teacher is meant to teach the truth to their students. If it was said out of spite for the children then it is a terrible thing but the teacher does have an obligation to teach the truth, in context (for example if a student asked how santa does it) the correct answer would be that it is physically impossible.
One side has been explained very well by others which is that a teacher should not ruin childrens imaginations and on that I can believe.
The other side of it is the definition of what a teacher is supposed to do, a teacher is meant to teach the truth to their students. If it was said out of spite for the children then it is a terrible thing but the teacher does have an obligation to teach the truth, in context (for example if a student asked how santa does it) the correct answer would be that it is physically impossible.