Well, technically that means "Na plaży jest piasek", which also seems like a better sentence, but it's not exactly the same from the grammatical point of view. The Polish sentence sounds as if someone asked "Where's the sand?"
If we're answering the Polish question, "Where is the sand?", then okay! Otherwise this is just weird
Yeah, it is weird, but that's how it was written. A less probable sentence than "Na plaży jest piasek", but obviously it's a correct sentence.
What is the difference in meaning between "Na plaży jest piasek" and "Piasek jest na plaży"?
The first one says what is on the beach, the latter says where is the sand. It's a matter of what is 'the new information'.