What does it mean when a guy friend kisses you on the lips?

danickor
The other night I was out with a bunch of my friends (guys and girls) and we were drinking together. When it came time for me to leave, I went to the door and one of my guy friends came with me to lock the door behind me. He thanked me for coming, and asked if I'd had a good time. Then he gave me a really nice, tight hug, looked at me for a second and kissed me on the lips. He has a girl that he is 'seeing' semi-seriously, and nothing like this has ever happened before. What does it mean?
What does it mean when a guy friend kisses you on the lips?
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