The fact you’ve got to learn them doesn’t negate the statement that they communicate without words.

All language has to be learned

True, though I think the point they're aiming at is that symbols like [new driver mark] contrast with literal pictograms like [symbol of person in wheelchair]. You can infer/guess the meaning of [symbol of person in wheelchair] 'without words' in a way that you can't with [new driver mark], because [symbol of person in wheelchair] is communicating with a picture instead, while [new driver mark] appears to be purely convention. (At least, the article doesn't seem to suggest otherwise.)