It is 'Creative License' at work. The author feels the question is more in the nature of a statement than in the nature of a question.
It can be any descriptor, and not just 'said'. It depends on what the writer intends to convey. For example:
'Why is it called a memorial?' said Laura'
Eliciting no response, Laura repeated, 'Why is it called a memorial?'
Infuriated at the nonchalant disregard, Laura shrilled 'WHY IS IT CALLED A MEMORIAL?'
But to answer your specific question: no, it isn't always Ok to use 'said' after a question.
A question can be said, asked, sputtered, gasped, wondered, interjected, whispered... it really depends on the context.
Is the usage 'correct'? Yes.
Is it good writing? You're the judge.Its hard to say with just one line in isolation. Perhaps a few preceding and following lines from the same excerpt (if it is an excerpt) would have helped establish the context better.