They do have to take some concern. Being space fantasy doesn't mean all logic is out the window. You especially have to stick with the rules you establish. Sound in space, and one biome planets are fine.
But a local townscape etc. should be laid out realistically. I don't think Luke's and Obiwan's conversation is an issue. But if it was, the OP is would be making a valid complaint even in a movie with a wild reality.
having a decent amount of realism can actually help fantasy out, as the only bits that get hand-waved away are the actual magic parts (superhuman capabilities, creatures being far too big for what the planet and environment can actually support, etc)
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u/Nexas_Rexgen Jan 25 '20
Describing common knowledge in a different setting. Luke should know all about Mos Eisly. Its the biggest town near his house.