If a guy "doesn't" know your real name is it because he's not that into you?

I was with my "friend" last night whom I have been "seeing" since oct 08. We were talking bout names I said my middle name was rose he said katrina rose, I was shocked. My name is kathryn. He said he didn't know my real name because he always called me kat. I don't know if I should take this offensive or not!
If a guy "doesn't" know your real name is it because he's not that into you?
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