Without casting aspersions on anyone's intelligence, I think it's a good idea to write what one actually means instead of writing an untrue approximation.

Mark Twain wrote, “the difference between the right word and the almost right word is really a large matter – it is the difference between the lightning and the lightning bug.”

In my reading experience, good writers use the right word, not the almost right word.

And he's wrong even if he did mean American deaths: the number of American deaths in WWII was 418,500 (see https://www.nationalww2museum.org/students-teachers/student-resources/research-starters/research-starters-worldwide-deaths-world-war). Even if he meant military deaths only (which he might have meant, since he does not write what he means), that number is 416,800, considerably higher than 300,000.

But perhaps he does not know how to use search engines. :)