Utter rubbish, you can use any single word command in the English language, another language with the judge's permission. That is ANKC Rules, Obedience trials all over Australia are judged under those Rules, or they should be........... My three OCs, in fact all my titled dogs in Victoria have the "drop" command............ "down" in our house means get down - from me or the furniture or wherever. Commands are only noises to dogs, it just helps if we use the same noise for the same action all the time. The excutive command judges must use as per Rules is "down" or "down your dog", most of us use a different word because we think it helps avoid dogs working on judge's command, but we all know that doesn't work, dogs aren't that silly!!!
There is only one exercise where a specified word must be used and that is "stay" in food refusal