My content unexpectedly appears on someone else's iPhone
I found some of my photos or health data appearing on others iPhone. When I helped my uncle to check his photos on iCloud, I found my photos unexpectedly in his iCloud, though it was my iPhone(Xr) before I sent to him, I already formatted it and logged in his iCloud account. And today when I helped my mother to set her new iPhone, after I logged in her iCloud account,I found there had an option which is backing up from my iPhone(Xr),I chose her iPhone(6 plus),which she had not used for years, to backup, but after that I still found some of my health data appearing on her new iPhone from her iCloud account.I need to know why and I couldn't remember if I logged my iCloud account on their iPhones