Yeah, so I'm guessing almost dying, resurrecting, and becoming a living magical sponge that can absorb people's mana at will might have effected his personality a bit.
It looks like an abridged version of the old "we came to the big city trying to find honest work, but it chewed us up and spit us out, and the only way we could make a living was through more and more evil deeds".
As for the "sparkling diamond" name my guess it's actually supposed to be "polished diamond", which in turn is supposed to be both a reference to the Aladdin movie and the general saying of a "diamond in the rough".
(I.e. they were crooks, but now they're reformed.)