What does the "you up' text mean from a guy?

This guy I barely know but think is cute was texting me in the evening, and we texted into the middle of the night, he was sending me selfies on the chat. I stopped responding at around 9 and then he sent me a "you still awake?" text. I said I was working on my college essay and then he didn't reply. Is this always a booty call text?
What does the "you up' text mean from a guy?
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