What he was saying in his talk was that his customers (people using Hey for email and calendar) never really wanted hybrid web-native apps, they want native apps (like most people prefer on mobile). His business could never afford to have a dev team that built and supported six different native apps, so they always built using hybrid web-native stuff using Turbo Native.
Now that his development team has access to agentic coding, they can build and maintain six mobile native apps. For his app, the back end part then becomes small and simple and they can reimplement it in rust to reduce server cost.
His point wasn't that rust is better than ruby, or anything like that. His point was that agentic coding allows smaller teams to do bigger things. For most people building on rails, their customers don't need native mobile apps (I know mine don't) and for them Rails is a fantastic choice for agentic coding.
Rails is so into agentic coding that they publish benchmarks of how effective different models are for building with rails:
TLDR: DHH isn't anti-rails, he is pro-agentic coding. Rails is great with agentic coding. AI doesn't mean layoffs, it means your teams can do much more than they could do before.