Actually, even the three layers above that are likely someone else's problem (data link,network, and transport). Full-stack usually means knowledge of the application layer i.e. HTTP and client side.
Honestly, I think that's extremely cheeky usage of the term. I'm of the opinion that you should be able to:-
- talk to a datacentre, get servers, switches, power, network racked and ready to go.
- Do the devops to configure this infrastructure.
- Understand data-layer requirements and generally host and manage a CP or AP system.
- Write the apps that'll live on these servers.
- Implement resonable caching to scale.
- Write the frontend code to implement a design to connect to these systems.
- Have enough knowledge to profile and debug the performance bottlenecks of such systems.
At about that point, you can start to consider yourselve "full stack". Now some could argue that you don't need rack the system or do the devops, but if you don't understand what you're hosting on, how are you ever going to debug an issue that outwith your application?
