Why is she mad at me?

[Has]

I am very good friends with this girl and we talk almost every day. Last night she sent me a text saying "hey, stranger" given we hadn't talked for 4 days and I responded "hello there. (her name), right? lol. how are ya?" and she responded "that was kinda rude but ok, I'm fine". I apologized of course and we sort of patched things up although I did it not know what I said that could have come off as rude, and she admitted to being bothered by it but never told me why she though it was rude. Anyone care to shed some light on this?

P.S. I don't know if it helps or if it has anything to do with this but about a month ago I told this girl that I liked her and she said she liked me back but didn't want a relationship now.