The official Linux packages for Sigil are generic packages. They're bundled in an InstallJammer installer and contain a number of libraries that Sigil depends on. This is not ideal but it's not possible to provide Linux packages for every distro.
I've created a wiki page which I'm putting together a list of Linux distributions that have their own Sigil packages. These are the best packages for users to install because they're smaller and tailored.
If your distro isn't listed and it has Sigil packages let me know and I'll add it to the list. If your distro doesn't package Sigil let them know you would like to see them package it. I'm always willing to lend a hand to get Sigil in more Linux distros.