When an app is uploaded to the app store, it is compiled for every different device separately. You likely have a higher resolution phone/device than the OP, so there's more image data on your version
Exactly. Older iPhone 6S here, showing 2.1 MB
I've noticed a differing pattern in our app: usually the newer devices (11 Pro Max) have a smaller foot print than older devices (iPhone 7 Plus) [1]