I think a better explanation is that Omni-man just snitched. Machine Head would never admit that he knew just because Omni-man told him, so we really would not know from that character whether or not he was actually telling the truth about having thought ahead. In fact, acting this way would be in his best interest by all margins. But I'm pretty sure they don't explain how he actually managed to get in contact with Battle Beast for a reason.
Omni-man being the mastermind behind the whole fight makes everything make much more sense.
From Machine Head's perspective, he gets to look incredibly smart and gets to send a message to anyone who would challenge him.
From Omni-man's never wanted Invincible to do this to begin with, and especially doesn't like the idea that his son is already ignoring him to go help random locals (remember he's being prepared to fight for Viltrum at the moment). So Omni-man, wanting to send a message, let's Machine Head know about this guy, finds him, and Machine Head teleports him in. Omni-man is the one who promised Battle Beast worthy opponents, because Omni-man is the one character who might have actually known who Battle Beast was and where to find him. He also has the benefit of killing the strongest members of the New Guardians. So it all worked out for him as well. And he'd never reveal this to Mark......why would he?
And Battle Beast is just a walking can of kicking ass. He only really tries to kill the people who do any damage to him whatsoever, outside of when he sees that Mark would kill the local guys. A subtheory of mine is that Black Samson got his powers back when he abandoned his suit, it was a mental lock not physical. And Battle Beast doesn't even attempt to kill any of the Guardians who didn't at least have super strength because he came purely to fight for honor.
We know that Omni-man was likely the reason for the Anonymous call, and it would make sense that he'd want Battle Beast to kill at least one of the strongest ones, since that would then provide an alternate suspect to who could kill the guardians. But Omni-man was watching from the beginning, and we just assumed he didn't say or do anything other than make that call.
It would also explain why Omni-man just watches as Battle Beast nearly kills Mark, but not actually kills him. Everyone acts like Omni-man would just stand aside because he couldn't beat Battle Beast, but at no point before or after this does Nolan just watch someone nearly kill Mark. I think he just talked to Battle Beast into just beating him up, and that's why BB tells him "killing you is an act of mercy."
He was both talking shit and also knew the real train that was coming towards the man, and that's just the beginning.