Why did my female friend stare at my chest?

My friend (female and straight) was staring at my chest for around 2-3 minutes while we were talking. I asked what's wrong and she said "oh, I was looking at your chest". I don't know why she would? I don't really have big chest as her,.
Plus we were wearing the school uniform (Normally I wear a baggy jacket, but I wasn't at the time. ), nothing revealing... She looked a bit surprised/interested when she was staring?
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+1 y
by the way, I'm not trolling.
Why did my female friend stare at my chest?
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