If they had intended the eggs to drop straight down all along, then there's a lot of completely pointless code in that routine, and that would be a lot harder to explain. I think it's pretty obvious from looking at the commented disassembly that the original intent was for angled throws, but whether it was changed to straight throws accidentally or intentionally is difficult to guess. The code certainly looks like accidental temporal coupling overwriting the register with the X velocity, but I can't imagine they wouldn't have seen that and fixed it in testing if it were unintentional.