The rule is about the implementation itself, but the other one is part of the benchmarking code. You'll need to be able to use the implementation, that doesn't

The rule is about the implementation itself, but the other one is part of the benchmarking code. You'll need to be able to use the implementation, that doesn't rely much on external libraries, with types from other packages. If you read the article, you'll find Julia is all about composing functionalities from different packages. Its a major driving factor behind the ecosystem - and usually not possible if your language relies on c libraries to do the heavy lifting.