Other-universe Batmen had indeed come to this universe before. But Batman himself was not someone who liked making a big spectacle, so after arriving, he had probably only operated in a few places. Ordinary people certainly would not have seen them.
At that time, Ma'lfak was probably still on Mars, while Zod was in the Phantom Zone. There was no way either of them could have encountered other Batmen here.
That left only one answer: Battleworld.
But Battleworld was not a place just anyone could enter. Ma'lfak himself was a nobody, a villain so obscure he could hardly have been more peripheral in the comic world.
Even in Martian Hunter's own stories, he had little screen time, much less any fans. Battleworld would never send him an invitation.
Though Zod was far more famous than him, he still could not compare to Superman's other arch-enemies, especially Lex Luthor.
Each hero's villains had, at most, one or two slots to enter Battleworld. Only the top dogs like Batman and Spider-Man were exceptions. No matter how the rankings went, Zod would not have made the cut.
If that was the case, then they should not have had any chance of meeting other Batmen. Yet they acted as if they knew those orthodox Batmen extremely well.
Schiller found that very strange, so he needed to spend some time investigating it.
First, he needed to find out whether Battleworld had sent invitations to those two characters. That was easy enough. Schiller directly called Lucifer.
"Hello? It's me. No, I haven't taken my annual leave yet. Even if I had, I still wouldn't travel with you, so give it up." Schiller coldly and mercilessly rejected Lucifer's travel invitation before getting to the point. "Did you send Battleworld invitations to Zod or Ma'lfak? The Kryptonian General,