iPhone X and iPhone 5c iOS 11.3 serious privacy and security wallet bug

I have an iCloud family account with my 7 year old son on the account, I had a flight to Berlin from London (travelling on my own), the outbound flight was on Eurowings and the inbound on British Airways, I have both apps installed on my phone and had saved the check in cards to my wallet, obviously when the flights were booked on Skyscanner website the BA flight had a return flight London to Betlin booked as cheaper than a one way flight, I wasn’t aware of that until I opened the Wallet app on my son’s iPhone and noticed a return flight with a future date in his wallet with my name, things got even more weird when I noticed that the BA card in his wallet is showing that I have Bronze executive club level when I actually have silver. Please note he does not have any of the airline apps installed on his phone.

Question: how did this happen?