HLJ has had this listing for a very, very long time. It's even older than their Figuarts listings. We've had this listing since before we knew anything about the candy toy medals set 2. Nobody's known exactly what it is in all this time and I don't expect that to change now without some kind of update first. The only thing it is certainly not is any of the DX O-Medal sets.
Cell Medals are intentionally not diecast. I'm sure part of it is a materials/cost issue, or perhaps another means of showing their inferiority to Core Medals, but the biggest reason is that they're used as projectiles in DX toys! RideVendor, Birth Buster, Candroids... All the gimmicks are weak already for safety reasons, and suggesting kids use plastic and diecast coins in such a way is asking for trouble.
If Cells were meant to have diecast, the DX versions would have used it, like the Cores.