The shorthand says one is cast and the other flow-formed. OZ’s own pages say both standard lines are low-pressure cast monoblock, made in Italy — the weight difference is the spoke design. Flow-forming is the separate HLT line, and telling HLT from non-HLT is the real buying trap.
OZ Racing: One of Its Wheels Is Made in Japan — and Only One
OZ consolidated to Italy-only production around 2017, with a single documented exception: the Japan-only Rally Racing 16, made by ENKEI. Which also means an older OZ wheel is not automatically Italian.