I don't think Reddit is so popular with steam people globally that they can push one team and suppress the others.
Reddit has about ~2 million uniques a day, and Steam gets ~7.8 concurrent at its peak.
Even if every Redditor is participating in this contest, they would make up slightly more than a quarter of people on Steam at any given moment. And I'm sure Steam's uniques count is more.
Reddit thought they caught the Boston bomber too...
It's not really that hard. The only thing it needs to be done it's a big push on one of the teams and things will snowball from there.