It had everything to do with BM, why do you think Minato and Naruto were the only ones with a chakra avatar ? What do they both have in common ? The Uzumaki seal.The sealing justu had nothing to do with how naruto looks
Where does the Uzumaki seal come from ? Hagoromo. Who is Hagoromo's son ? Ashura. What does the chakra BM look like ? Ashura's avatar. Who is Ashura ? The Uzumaki's progenitor. Do the math.