I mean, yeah, I still don’t understand why Luke abandoned him on Pasaana. But I don’t see how this line explains that? All this line tells us is that Leia and Lando are in communication, which just adds more layers of convolution, imo.
Like I said though, if we could flesh out the scene to give Lando some actual development, that would be swell; but that’s a separate issue from this one line.
There’s nothing in the film to suggest he’s been there the whole time. The transmission implies he headed over there when he heard they needed help.