That is not the article on Agent Orange, but rather a C-quality-rated article you've cherrypicked with significantly more political bent. This is the wikipedia article on Agent Orange: https://en.wikipedia.org/wiki/Agent_Orange:

Agent Orange is an herbicide and defoliant chemical.

Furthermore, this question was actually litigated and decided "not a chemical weapon" in the US. Again, from the wikipedia article on Agent Orange (emphasis mine):

"Three judges on the Second Circuit Court of Appeals upheld Weinstein's ruling to dismiss the case. They ruled that, though the herbicides contained a dioxin (a known poison), they were not intended to be used as a poison on humans. Therefore, they were not considered a chemical weapon and thus not a violation of international law. A further review of the case by the whole panel of judges of the Court of Appeals also confirmed this decision. The lawyers for the Vietnamese filed a petition to the U.S. Supreme Court to hear the case. On March 2, 2009, the Supreme Court denied certiorari and refused to reconsider the ruling of the Court of Appeals."

No matter how you feel about Agent Orange the original article's statement about dioxin is just factually wrong.