I suspect that a comment that had some minimal comment other than just an upvote note might have been better received. Examples would be something like "I understand your position. Upvoted." or just "That makes sense. Thanks for clarifying." Although I did make a comment that was almost identical to the second one a while ago that got downvoted.
Edit: See for example this comment by Pedanterrific which seems to have been intended to have a similar goal set.
Thanks. I guess a possible reason why it wasn't well-received was because maybe it read as "Hopefully he'll trade rep with me =D" or something. Perhaps any upvote declaration would suffer from that, but especially one that doesn't have any other content to distract from it or warrant an upvote on its own.
See: You Be the Jury, The Amanda Knox Test
While we hear about Bayes' Theorem being under threat in some courts, it is nice to savor the occasional moment of rationality prevailing in the justice system, and of mistakes being corrected.
Congratulations to the Italian court system for successfully saying "Oops!"
Things go wrong in this world quite a bit, as we know. Sometimes it's appropriate to just say "hooray!" when they go right.
Discuss, or celebrate.