Huge speculation time !
So the monitor asks for 7 heroes ... and they are not any of the arowverse ones. Like Smallville, Brando Supes, Batman, 90's flash and others... so they have the stand on supergirls earth.
But they got fucked up baddly and then in earth 1 the arrowverse team has to do it
I would suspect the idea is that the 'ideal' team would be straight up the Justice League, but they'll only be able to cap out at Superman, Batman, the Flash, and arguably Martian Manhunter, and even then, the examples they find have issues to them. Thus they're forced to make do with the Arrowverse crew.