3 things:
1. Officials don't watch events like a fan, they look at them, which is not as much fun. The ref in that race was obviously watching and failed to raise the flag.
2. Stepping out of your lane happens more than people realize. When I officiated, I could raise the flag on half the 200m races. 'Unofficially' or personally, I don't have a problem if it is one slight step over and it does not impede the other runner. The biggest issue is the lack of consistency, the Brits and the French to a lesser extent will raise the flag ever time especially when it involves a race when their athlete are competing. They will never give USA athletes a break when it comes to any type of rules violations.
3. For those who have never run the 200m, staying in your lane is not as easy as it looks. It is not just about running twice the distance of a 100m, the turn adds a different dynamic. Unless you are a 200m specialist and/or you have been running it since childhood, you actually need to look down and focus on staying in your lane. Look at Isiah Young, Michael Norman, Ramil Guliyev and some of the 200/400 athletes for what a smooth 200m turn should look like. If you watch some athletes, you see uncomfortableness on the turn by nearly crossing their right leg over their left leg fighting to stay in their lane.