Nothing strange here.
To be clear, Holocaust death toll by Apr 1943 was around 4 million according to orthodox historiography (1.5 mil killed by SS police, 2 mil in Reinhard camps and Chelmno, plus many from privation) so the crude estimate isn't that far off.
Also the article gives a rationale for how Unger arrived at the number. His methodology is clearly flawed but I don't see anything strange (conspiratorial?) about it.
It should be said that the Nazis referenced the "6 million" as well