It's pretty easy to prove for yourself. Especially if you can open up different tabs in your computer. Here's how to do it. Find a user who's made a comment sometime in the last month that you haven't yet voted on (points don't count for votes on memes or comments more than a month old), open their profile in one tab, where their score is, and in another tab, open the meme with the comment on it.
Click upvote on the comment, go to the other tab, refresh the page, and you should see that their score has increased by 30 points. You can double-check by going back to the comment, removing your upvote, and then when you go back to the other tab and refresh the page again, the 30 points you added to their score should be removed. Then you'll know it was from your vote, not points they received coincidentally for something else at the same time.
(It works better if you try this on a user who doesn't have a meme on the front page currently, and who isn't currently on the weekly leaderboard. If they're possibly receiving other points while you're upvoting them, it will make it harder to be sure.)