King Erichthonius of Dardanian was very rich. He had 3000 mares some of whom were made pregnant by the North Wind. Twelve horses were born. Nowadays we call foam on top of waves on the sea white horses. Maybe this legend came from a similar concept. And when the wind causes the wheat in fields to ripple it they could have imagined the horses running over them.
αἳ δ᾽ ὅτε μὲν σκιρτῷεν ἐπὶ ζείδωρον ἄρουραν,
ἄκρον ἐπ᾽ ἀνθερίκων καρπὸν θέον οὐδὲ κατέκλων:
ἀλλ᾽ ὅτε δὴ σκιρτῷεν ἐπ᾽ εὐρέα νῶτα θαλάσσης,
ἄκρον ἐπὶ ῥηγμῖνος ἁλὸς πολιοῖο θέεσκον.
When they galloped over the grain giving fields, they ran over the ears of the wheat and did not trample it, and when they galloped over the broad back of the sea, they ran over the top of the breaking if the grey sea.