This is correct.
"Once upon a time, long ago, the Koroks took on human forms, but when they came to live on the sea, they took these shapes. Now they fear people... but to me, they will ever be my cherished little children."
Direct quote from Wind Waker.
It does specifically say "when they came to live on the sea" but that doesn't mean this isn't a form they use for other means too. It could be purely to spread seeds around Hyrule in a quicker way (being more able to traverse the land by flying around in the winds). Obviously they trevesed the great sea in this form to take seeds to different island but in BoTW they could be spreading the seeds to try to help Hyrule flurish again after... although nature seems to be doing pretty well by it's self.