Xcode organizer shows crash reports of unsupported device
iPhone-only apps can be downloaded from the App Store to an iPad regardless of whether or not you support using it the iPad.  This is different than iPad-only apps because those can't be installed on an iPhone (non-jailbreak).

A user simply has to select to download the iPhone version to their iPad and they can download it.  The app will display on their iPad in 'compatibility mode', that's as a smaller (screen size) app or magnified to fit the iPad screen.

Just because people are using iPads doesn't mean you have to provide them support.  You can always refuse support to someone if they've used your app on an 'unsupported device'.  Just be sure to clearly call out that it's not designed to run on iPads in your app description.

In iTunesConnect, you're only seeing users who have approved to share analytics and logs with both Apple and the app's developer.  That audience might only contain people with iPhones that agreed to share the logs so you're only going to see iPhones in the logs (this is why I use a 3rd-party analytics tool in addition to the regular ones from Apple).