Seen sister topless while tanning?

ok this sounds perverted but please dont take it perverted im 14 my sister is 16. we have a pool and its fenced in with privacy fence our parents work and we're out for the summer of school. well my sister was tanning i looked out and seen her tanning and thought it would be a nice day to swim so i get ready and walk on back deck to pool when i go outside my sister asks if i could get her something to drink. i go to fridge and get her something. she was tanning with her straps un-tied laying on stomach or ever how girls tan like that when she raised up to get drink i was handing her she was topless she took a drink and sit it down on a stool thing she had then laid back down. i've accidently walked in on her before in the past by accident but this time its like she didnt care and raised up and got drink and laid back down. it just kinda threw me off for a second, has anyone elses sister went topless in front of them or is this weird? should i tell my parents? or is it no big deal