I don't like the theory that the black hole sent everything to Caliborn, because then, it would mean that Calliope would have had Yaldabaoth as a Denizen, not Echidna. Or that would mean the explosion happened on Jade's planet in the Doomed Timeline where Calliope enters the session.

Well, the thing is- Alt! Calliope was never in contact with anyone from the Alpha Group. Without Calliope, Roxy and Dirk would’ve stayed disconnected from Jane and Jake, they would’ve never been able to even start the Session of SBURB and get to know each other. There was never a Black Hole to send Yaldabaoth to Calliope in that Alt Session, because she’s… From a Doomed Timeline. In which she predominated over Caliborn. A Doomed Timeline where Lord English was not born, and as such all of his Time Loop is unravelled and couldn’t go too far.