Yes, there's no logic to it but “más X que nadie” means the same as “más X que todos”, for any value of adjective X. If there's a difference, it's very subtle.
- “Más lista que nadie” = she's smarter than anybody that you can think of; nobody is or could be smarter than her.
- “Más lista que todos” = she's smarter than anybody around, smarter than every person that here and now could compare with her.
- Also possible, but different meaning: “Más lista que todos ellos juntos” = she's smarter than all of them put together.
The principle is valid also for nunca: “Me siento mejor que nunca” = “Me siento mejor que en todo otro momento; nunca (antes) me había sentido mejor”.
I'd say this is ground-level Spanish, so to speak, i.e. something shared by all dialects.