Yes, it definitely looks like you've installed via synaptic. I was unaware they were that recent with Sigil.
And by all means ... if you're comfortable with the version you have (and you're not the adventuresome Linux aficionado) then stick with Synaptic. Your friend is right. The official repos won't steer you wrong. And if you're lucky enough to have a distro that keeps Sigil fairly up to date, there's no reason for you to jump through a lot of hoops update.
