I think the parent was assuming you did most of the development yourself. Judging by what's been said, it's more likely that your contracted developers themselves own the IP, not either of you.
The contract with developers states that Jim will own the finished product. My role in the app development was to make the initial sketches & app flow (both in the beginning and during the development), some design stuff, and Android testing, so I guess it can be argued that Jim doesn't own 100% of the current app because I've contributed something to the development as well
Yeah that’s quite a bit dicier. I did assume you had done the actual development. Copyright on visual presentation is much more difficult to argue your case with.