The language and title of the article seem a bit loaded, though there isn't any reason to question the basic facts of the article.
While it is true that entire islands were blown away and lagoons contaminated with waste from test detonations there was probably only one blast that probably directly and permanently impacted people in the area: Castle Bravo.
Castle Bravo was a test failure that made the Bikini Atoll famous, because the explosion was stupendously larger than the planned detonation. That test was supposed to be a secret experiment, but because it was so large it became an instantly known international incident. Wikipedia says the planned detonation was 6 megatons, though video documentary puts the planned detonation at closer to 4.5 megatons. Even still it would have been the largest man-made explosion to that point.
The actual explosion was somewhere between 14.5-15.5 megatons. The failure was a misunderstanding of basic chemistry under nuclear conditions. Scientists knew at the time that explosive force could be multiplied by an order of magnitude by wrapping a nuclear bomb device in fissile material thereby creating a multi-stage detonation. The first stage is the nuclear bomb itself and the second stage is the reaction of the fissile material to the intense heat and pressure thereby becoming fuel for an additional layer of explosion not used by the initial nuclear detonation.
The reason for a multi-stage devise is that a nuclear core has a specific job and the fuel of the second stage would not help achieve that job. The second stage only becomes valid once the first stage is complete. But that second stage fuel isn't stable. It is a rapidly decaying material, which in this case was radio isotope lithium 6. To increase stability the second stage material was wrapped in a blanket of lithium 7. lithium 7 is a heavier radio isotope, but it does not decay in a way that makes it a fissile material. Specifically, Lithium 6 decays into tritium when bombarded with neutrons and tritium is a very unstable radio isotope of hydrogen with 3 neutrons that is the core of the infamous H-bomb.
What scientists didn't know at the time is that under the heat and pressure of a nuclear detonation lithium 7 sheds a neutron and rapidly becomes lithium 6. That effectively means Castle Bravo was the first 3 stage nuclear bomb where all material supplied decayed in a specific order to become fuel in separate stages and each stage magnifying the explosive capability.
Local islanders were impacted by that detonation, but so were many American observers and scientists 30 miles away. The local islanders, and a Japanese fishing vessel, were further away than the Americans in that area, but were in the path of high altitude wind flow. The largest environmental failure from this was the inability to contain the resulting toxins. Trace amounts of fallout would eventually reason Japan, India, and the US. The entire local region was contaminated in a way that would only be understood or measurable over decades due to the increased presence of heavy metals in the ground and water resulting in toxic food supplies and heavy metal poisoning.
* Castle Bravo - https://en.wikipedia.org/wiki/Castle_Bravo
* Radio Isotopes of Lithium - https://en.wikipedia.org/wiki/Isotopes_of_lithium
* Bikini Atoll - https://en.wikipedia.org/wiki/Bikini_Atoll
* A good video documentary - https://www.youtube.com/watch?v=qM4ZYQmFGlw