Why did the android remark on Aurora's beauty?

The first person and probably the best one to comment on a character is the actor himself, I presume. Please find this comment by Michael Sheen himself in the given link below where he explains how the Android character Arthur was programmed to be pleasant and well mannered just like an experienced bartender would be. So for your ques there are two possiblities:

1. He could access the database of the passengers (it also seemed he knew them prior to when Chris talked to him) and was able know how to greet them from their profile description, age etc.
2. Secondly this might have just been a by default addressing approach for a young female who approaches the bar.

The comment by the actor:

Affable Arthur is programmed to please, explained Sheen from Los Angeles, whether it’s shaking the perfect Manhattan, telling a joke or offering a sympathetic ear. He and director Morten Tyldum (The Imitation Game) spent considerable time discussing how Arthur would be programmed to make his customers happy, anticipating their needs and learning from them as he went. But human nature is a tricky thing for a robot to puzzle out.

I've had websites tell me they're "glad" I'm back. According to science, Websites can't feel emotions either. But someone programmed the website to say it's feeling "glad" I'm back.

Arthur has the same kind of programming.