It says Cambodia has 74 characters, "the most of any language in the world". That sounds wrong. Hindi's Devanagari has 100+ characters, though some are certainly related to each other.
It's definitely wrong. The misconception might come from the fact that Khmer Script used to hold the official title of "alphabet with the most letters". It has since been reclassified as an abugida, not an alphabet, but many sources still proclaim it as the world's biggest alphabet.
> Wouldn't the various Chinese languages, and Japanese scripts, have way more characters?
It depends on how you define "character", I guess. The hirigana or katakana "alphabets" have 48 characters. These alphabets map best to the western use of characters.
Kanji is probably what you are thinking of, where each word in Japanese gets its own "character". There are ~50,000 different kanji symbols.