Nordquist made the remarks on the Public International Law Colloquium on Maritime Dispute Settlement, held in Hong Kong on July 15 and July 16.
He said the tribunal made a "very bad decision," for procedural reasons, to keep the case before it, and that the award is a "huge mistake," and should be "criticized severely."
Nordquist also questioned the tribunal's conclusion that Taiping Island, among other "features" in the South China Sea, is a "rock" rather than an island.
If Taiping Island was recognized as an island, it would be entitled to 200 nautical miles of exclusive economic zone, plus the continental shelf.
The zone would then have covered every single maritime feature that was in dispute except Huangyan Island, said Nordquist.
If this was the case, then the disputes would be concerning maritime delimitation, over which the tribunal would have no jurisdiction, he said.
And that's why the tribunal had been trying to deny the fact that Taiping Island is actually an island, by narrowly and improperly construing relevant articles in the United Nations Convention on the Law of the Sea (UNCLOS), he said.