Hi,
Yes, the only thing you can download with Safari on iOS is image. This is because iOS does not expose file structure to user (download file to somewhere user can never see does not make any sense), it has nothing to do with what you did or what we did in HikaShop. Browser on Android can download arbitrary files because Android file structure is visible to user. So I'm afraid you can do anything about this.
Here is a previous discussion on Apple community:
discussions.apple.com/thread/3697948?start=0&tstart=0
The ONLY thing you can save to an iPhone, from Safari, is a pic. Nothing else, and no downloads.