When I went to the photo studio to take pictures without linking any of his devices, why were the pictures automatically transferred to my mobile phone?

This is because the photo studio uses wireless transmission technology.

There are some cameras and photography equipment on the market that support wireless transmission. They can transfer photos to designated devices through Wi-Fi or Bluetooth. Before you go to the photo studio to take pictures, the staff is already there. The wireless transmission parameters are set in the device and your phone is paired with the device, so any of your device photos are automatically transferred to your phone without linking them.

After shooting in the photo studio, the staff can send the photos to your mobile phone through wireless transmission.