The app requests sandboxing. That request then causes it to be run in a sandboxed environment. Apps can refrain from requesting it and run non-sandboxed, but such apps are not accepted in Apple's store.
I can see why one might think that, but it's not the case. The core requirements for the store are optional things that can be added to any app: sandboxing and code signing. Apple just enforces those by refusing to accept any app that doesn't have them.