Do you think that maybe the reason there was 2 frog temples on alternia was because there was another session played on it? And how likely do you think that the session was done in hiveswap?

There was no other Session because the two Temples were actually a single 12-Player Session Temple split in two. If there had been a Session before the Trolls, Alternia would’ve been destroyed- Unless it was a purely Void Session I guess? 

Either way, what the 2 Frog Temples may imply, is that there may have been two First Guardians on Alternia, which does give some sense to the Axolotl Concept Art.