Comment by FrostKiwi

Yes, that also surprised me and I tested it on multiple mobile Apple devices. It's not really a mistake per se, the implementation is free to do what it wants. Selecting MSAAx2 on these types of mobile GPUs simply has no upside and isn't really supported over MSAAx4 and I guess apple still wanted to make the choice somehow possible, as opposed to Android, where there is only an illusion of choice.

It's just so happens to produce visible artifacts in this case. I suppose for 3D scenes it's mostly fine.