Rittenhouse was a reckless fool whose recklessness and foolishness ultimately left two people dead and one wounded.
The verdict says that 12 people - the ones whose opinion count in the legal system - were not sure beyond a reasonable doubt that his fatal actions that night were reckless and foolish in a way that violated Wisconsin law (edit: at least with regard to the specific laws he was charged with breaking).
His actions still aren't praiseworthy.
I get the impression that many of those hailing him as a hero are either far-right reactionaries who are simply doing so to be diametrically opposed to prevalent leftist sentiment about him or supporters of violent vigilantism and excessively lax gun laws.
It's another episode in the larger series of intellectually hollow, emotionally charged tribalism that has been looming over U.S. politics for at least five years now.