The line is so vague though…half the people here took it to mean that Leia contacted him because he was already on Pasaana, and the other half took it to mean that Leia told him to travel across the galaxy to give some exposition about Ochi, and then bugger off to do God knows what instead of helping the gang. If you remove the line, you can still believe whatever you like. Just like you do already. (And the canon answer is that he has been on Pasaana this whole time anyway. I don’t care about canon so much *cough* spice-runner *cough*, but I know that Hal does.)
And seriously, the movie is definitely trying to make Lando’s identity a dramatic reveal, right? Am I crazy? Let’s help them with that.