But he literally says in the scene, “Leia sent me a transmission.” The implication is that he was informed about the heroes picking up Luke’s search, and went to meet them at the festival.
I don’t really have a problem with Lando’s scene in the desert. Cutting it makes Lando’s appearance even more random, and it contains some important exposition about the hunt for Ochi.
I felt like the implication was “Leia told me you were swinging by” more than “she told me to meet you, and that’s how I got here way before you did and found a way to blend into the culture when she only realised you were coming here right before you set off.”
The randomness of him showing up after his best friend’s widow dies is less than him living in the desert for 30 years, but that’s just me.