One way to hold upturned is to picture something being rotated until one of its surfaces ends up facing the sky. The word tells you the turn happened; it leaves you to work out which surface won. Tip a face back and the front of it aims up, so you get an upturned face looking at fireworks. Curve the end of a nose or a roof and only that small tip aims up. Roll a box right over and it is the underside that ends up on top, so the whole box is upside down. Same turn every time, different part of the thing pointing at the sky — and that single difference is what splits the word into its two meanings.