This is an accepted solution.
I believe that's the iPad emulator from appetize.io. Are you attempting to reproduce on an iPad as well?
Thanks @_JB! Yes - my app got rejected and the app reviewer didn't respond to my email asking for more information so I could reproduce, so I was navigating in the dark. That said, I ended up already resubmitting without using the shopify_app gem so at this point this isn't blocking anymore. I appreciate the help.