Supposedly, the code was created by the "Defending Digital Democracy" project. Robby Mook consulted the project, but claims that he did not develop any code directly.

“Sorry, folks. I did NOT have anythjng to do with building the Iowa caucus app. I dont know anything about it, had no role in it, and dont own a company that makes mobile appa. Please contact @iowademocrats with questions about it.” - Robby Mook

https://www.dailydot.com/layer8/robby-mook-iowa-caucus/