Am i a pervert, why would my sister do this?

My parents work and we was home alone, I sleep late since we're outta school for summer, usually stay up late playing video games, im 14 my sister is 16.About a week ago well I woke up about noon and went to the bathroom i open door it wasn't locked. When i open it my sister was standing there topless looking in mirror. i just shut door and through the door i said oh sorry the door wasn't locked i was gonna get in shower. She opens door walks out and says go ahead i was examinning my tan lines. She started telling me how she bought this tanning package and was tanning topless and trying to see if the lines were going away. The thing is she was still topless while telling me this then she walks outta bathroom and to her room without a top on. I was like WTF???? As she has never really done anything like that before we've bumped into each other by accident before, but it's like i accidently walked in on her without a top and she didn't care and tried to carry on a conversation. Well today was kind of a similar incident i see her i said dang your face is red. She said yeah they put new bulbs in tanning bed and i stayed in their too long, my back stomach and chest are worse. A little bit later i walk down hall and she has door open to bathroom looking in mirror rubbing aloe lotion on herself while topless. She tries to carry on conversation again saying see i told you my stomach was worse she is telling me this while her boobs were out, then she turns around and shows me her back. I just said yeah your red. I couldn't help but to look i feel bad for looking i feel like a pervert for looking, but why would she do this?