Unfortunately people often don't stay calm and think rationally in such a situation. One panics and adrenalin starts pumping - and the person just reacts instinctively.To be honest - and this is tough to say because most would react as Denis did when confronted with thieves - your car is not worth your life - and too bad he simply could not have turned from the scene of the crime and ran to the cops.
When he decided to confront and intervene, it cost him his life. For mirrors on a car. It was not worth it - he should have let them steal the whole thing and stay safe.
Over side view mirrors he is dead. Incredible.