It's really surprising that this and the Banqiao dam failure that killed 230,000 are fairly unknown to the west while Chernobyl is a household name, which killed ~60 first responders and "up to 4000" from early cancer deaths (using conservative linear no threshold models of dose response) https://en.wikipedia.org/wiki/Banqiao_Dam
According to the HBO series on Chernobyl the Russians deliberately kept no statistics on radiation related illness and deaths related to the accident. They said estimates ranged from the number you quoted to upwards of 90 000 deaths. Thanks for telling us about the Banqiao dam failure I will read more about it.
Huge amounts of radioactive krypton gas were "vented", and, being much heavier than air, it all ran downhill and pooled invisibly at the nearest dam where, conveniently, only poor people lived. No effort was expended to warn or evacuate them, or to catalog the deadly maladies they suffered in their thousands afterward.
To this day it is easy to find people insisting in all earnestness that TMI didn't kill anybody. They are never interested in discussing the gassing of the downstream population.