Buddha's birth story is it myth or legend?

I’ve heard that some people went to India, unfortunately they started to doubt that the Buddha really exist when they saw some carvings & painting of the Buddha’s birth such as the image of the Queen Maya giving birth to the Buddha from her side, or after birth, the “baby Buddha” began to walk seven steps forward and at each step a lotus flower appeared on the ground. Then, at the seventh stride, he stopped and with a noble voice shouted:
“I am chief of the world,
Eldest am I in the world,
Foremost am I in the world.
This is the last birth.
There is now no more coming to be.”

​Where does ​all these ​myths or perhaps ​legend​s​ come from?​ ​Hinduism?
​Apparently we can find this​ story​ in DN 14​ too​. So, the next question would be, is this sutta authentic?​
If it is what is the meaning to the story?

Compare the story to MN 64:

Mālunkyāputta, to whom do you remember my having taught these five lower fetters in that way? Would not the wanderers of other sects confute you with the simile of the infant? For a young tender infant lying prone does not even have the notion ‘identity,’ so how could identity view arise in him? Yet the underlying tendency to identity view lies within him. A young tender infant lying prone does not even have the notion ‘teachings,’ so how could doubt about the teachings arise in him? Yet the underlying tendency to doubt lies within him. A young tender infant lying prone does not even have the notion ‘rules,’ so how could adherence to rules and observances arise in him? Yet the underlying tendency to adhere to rules and observances lies within him. A young tender infant lying prone does not even have the notion ‘sensual pleasures,’ so how could sensual desire arise in him? Yet the underlying tendency to sensual lust lies within him. A young tender infant lying prone does not even have the notion ‘beings,’ so how could ill will towards beings arise in him? Yet the underlying tendency to ill will lies within him. Would not the wanderers of other sects confute you with this simile of the infant?”