The throwing is relevant because the mob in question has a very well documented history of throwing molotovs, bombs, or bricks at things they don't like. If any semi-lucid person saw an antifa/BLM rioter throwing an unknown object or container at them, the first thing they'd think is "they're trying to kill me".
The fact that something was thrown by a rioter means he had every right to reasonably believe his life was in danger, which is pretty much all that's required to get acquitted. Without the thrown object his case is much weaker, because they can always make the bad faith argument that an unarmed person couldn't possibly be a match for someone with a gun, therefore he had no reason to believe his life was in danger.
You have to remember that 90% of people believe real life works like a movie. They think unarmed equals non-lethal. That's why "unarmed" is one of their favorite words. To them, it's synonymous with "harmless". They've never been punched, never been kicked, and never been within ten blocks of physical violence in general. One hundred percent of their "experience" with unarmed combat is in movies, where the only time anyone dies in hand to hand combat is if their neck is snapped or they fall off a cliff.