Um, - not always. I disagree with this particular take as it does not constitute a reliable rule. For example, as a well known counterexample, Epiphone builds several guitar models to the same dimensions and (mostly) same specifications as their Gibson counterparts. Nevertheless, most guitar players I know say they are not actually equal and do not produce equivalent results in fact - i.e., they do not sound and play the same.
Thus, looking, sounding, and walking like a duck does not always mean it is a duck. N'est ce pas?
James