Twain was not above using hyperbole to make a point.
I see the same sentiment as here as well as Non Fui Fui Non Sum Non Caro...
VS47. I have anticipated you, Fortune, and entrenched myself against all your secret attacks. And we will not give ourselves up as captives to you or to any other circumstance; but when it is time for us to go, spitting contempt on life and on those who here vainly cling to it, we will leave life crying aloud in a glorious triumph-song that we have lived well.
Twain's quote tells me there's nothing to fear in death, no care, nothing to be worried about.