That is a common fallacy but is not true at all. There is a pretty long list of exceptions to it such as some of these which could be applied in this case:

- The court recognizes that by law the declarant is not required to testify;
- The declarant refuses to testify;

Some other exceptions which may or may not apply:

- It has sound guarantees of trustworthiness
- It is offered to help prove a material fact
- It is more probative than other equivalent and reasonably obtainable evidence
- Its admission would forward the cause of justice
- The other parties have been notified that it will be offered into evidence

That's just a handful. So yes, hearsay can be admissible. In this case much of it was corroborated between a variety of witnesses which gives it much more weight.