It's certainly in need of a second version and some editorial oversight but I think the core is good. For example under the "what do these hand signs mean" part I was expecting the OK sign to also say "wanker" as with movement and orientation this is a UK version. OK is definetly out of use here (as a hand sign) and thumbs up is quite childish/dated (like saying "fab").
As far as the 'thumbs up sign' goes, it's still common enough that it's hard for novice scuba divers to remember that it means 'ascend now' rather than 'everything's OK'.
* Winston Churchill probably used the palm inwards version until it was explained to him that it was a rude gesture.
* The 'archers' explanation is very likely wrong.
* You hardly ever see it in England nowadays, it's been replaced by the single middle finger.
As you say, it makes you wonder how reliable the rest of the article is.