Why is truncate DDL?

Question

I have an interview question, which was asked during my interview. I answered the question, but interviewer was not so convinced with my answer. So, anyone please correct me with my understanding ?

Q. Why Truncate is DDL Where as Delete is DML ? Both do almost same job (removing rows)

Ans. When we are using Truncate, we are de-allocating the whole space allocated by the data without saving into the undo-table-space. But, in case of Delete, we are putting all the data into undo table-space and then we are deleting all the data.

Please, if anyone knows best answer for the above, please explain.