It is used casually as "Hiya, you OK?" It doesn't necessarily mean that the speaker thinks there might be something wrong with you and wants to check, it can be taken to mean the same as "How are you?" You'll also hear "Hi, you all right?" in the same way. I don't recommend that learners use it unless they are near fluent and can say it in the offhand, casual way that native speakers do.
I doubt that the girl who spoke to you was enquiring after your actual health any more than someone in the UK who says "How are you?" is. Generally, the polite and expected reply to that question is "Fine, thanks. And you?"
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