Note that I've obviously never written an iOS app, but I figured that Apple required you to submit the source of your app for their auditing process. Which sounds extreme, but this is Apple we're talking about. :)
There was indeed a rule at one point that apps had to be written in C, C++, or Objective-C. This was allegedly implemented in order to ban cross-compilers such as Flash compiler[0]. Presumably they would either require the source code to verify this, or inspect the compiled binary for some identifying feature. However, these rules don't exist in the current version of the guidelines[1].
This rule got so much press 7 years ago that it will be one of those "truths" about a platform that never dies on internet forums, that and the Playstation platforms using OpenGL as their primary API...
