I must have misspoke, 'drop up', as per Win 95 onwards is anti-pattern to me, everything menu-wise that is drop-down is good, again to me, given that is the UX I learned first with WIMP GUI's.
But why? It seems highly arbitrary to me that drop up is bad and drop down is good.
Drop downs make more sense because you always read from top down.
“drop up“ is quite natural when you trigger the menu with a key on the bottom row of the keyboard. Classic Windows UI (grumpy old me does not want to talk positively about anything since the ribbon bar) was always strongest in "combined arms" mode, mouse use on the right coordinated with the left part of the keyboard. (Whereas the Apple style seems more polarized to me between easy mouse-only and powerful keyboard-only "modes", with not much in between)