Ping the B.S. filters on maximum bandwidth! How many kids eat tuna fish that much? My guess is very few who like it. This smells fishy to me.
In the article, the boy did this rather than eating junk food. Sounds like junk food would have been healthier.
Maybe the key point of the article is that anything should be taken in moderation -- too much of anything can be bad.
I have known women who want to stay thin that eat a can of tuna a day -- especially when trying to bulk up (distance runners, etc).
I knew a man who ate tuna fish 3 times a day, as well as a sort of porridge. It was some diet regimen he had developed himself. And - every year I saw him - the mental deterioration was noticable.
Of course it might have been from some dietary deficiency rather than mercury poisoning, so I'm still agnostic about Hb's role. But singularity diets are - in general - always dangerous IMO.