You’re confusing concurrency with parallelism. A single-threaded event loop a la node is indeed concurrent. Multiple threads a la the Kotlin IO pool you mention

You’re confusing concurrency with parallelism. A single-threaded event loop a la node is indeed concurrent. Multiple threads a la the Kotlin IO pool you mention would be both concurrent and parallel. Concurrency isn’t about different parts of the code actually executing at the same time, merely about being able to structure and think about code as if it were executing that way.