I'm not sure what you mean by "its opening a zip file for them without installing it". You did upload a ZIP file though. I recommend uploading an .apk file directly since apk files are already compressed
Some devices may have security settings enabled that prevent installing an APK file. The owner of the phone may have to configure their phone. Also, although it is possible to upload an APK file to android, generally if you want the best user experience then you're best off adding the game to Google Play, then adding the link to your itch.io page.