Jim Lindgren says he "endorsed" them. But a closer look at the linked article seems to indicate that Castro was only making a political prediction as to the likelihood and electability of such a ticket. Specifically, Castro says it would be "unbeatable"--though where Castro gets the expertise to know how one wins a contested democratic election remains a mystery (certainly, it's not through personal experience!).
The mistake looks to be an honest one, and as Professor Lindgren says, even if Castro was offering his "endorsement", it wouldn't say anything about either Clinton or Obama, neither of whom sought it. But still, even in this very minor form I don't think the story should be overblown.