In vitro studies demonstrate similar toxicological damage on human tissues from both compounds — even according to your linked article. The toxicological profile of the two substances differs mainly in half-life in the human body.
A shorter half-life doesn’t make ethyl mercury safe in any objective sense. There is no such thing as a safe dose of mercury.
And as I mentioned earlier, some humans are outliers; they can’t rid themselves of ethyl mercury nearly as rapidly. Genetics plays a role here.