Palm trees, like this Phoenix roebelinii (pygmy date palm) grow from the center. To determine the robust health of a tree, look at its "spear" leaves in the middle. They start out all clumped together, with that powdery residue, and then open up.
I have had palms here at The Tropical Paradise for twenty years, and no, I have no idea what the botanical reason for the white powdery residue is. I am satisfied in knowing that it means a wonderfully healthy tree, and that that is how God made it.
By the way, if you have a healthy tree that is throwing up several spears, go ahead and do a gentle shake to open up the fronds. You will see that powdery residue, which falls off, and mostly you will see some beautiful leaves!