I haven't tried since I don't have a twitter account, but I'm assuming that yes, it would post his own comment, and a link to it (because there would be absolutely no point to it otherwise). And therefore a link to mine too.

And he can still share any post of mine with one click using that little "share" button at the top of the page.

ETA: Example. (http://dysonrules.livejournal.com/200879.html)