How was Erichthonius and Hephaestus SonDaughter related to Athena?

It's an interesting story.

Athena visited Hephaestus once to ask for some weapons, but he thought that she had come to seduce him, and he attempted to rape her. Athena managed to escape, and Hephaestus ended up fertilizing the earth. Later, Erichthonius was born, and Athena hid the baby in a box and gave it to the three daughters of Cecrops.