To me the concept doesn't even have to mean that individual is outputting 10x amounts of code or closing 10x stories...
More so it means that there ideas, abstractions and frameworks result in substantially higher productivity for anyone working on the project than the average dev.
Beyond just the talent to do this successfully, you also have to give people the space and freedom to actually do 10x work... This tends to extend well beyond the narrow scoped requirements written in the current sprint of tickets.