Pretty much correct, yes. The node.js server has an internal thread pool so it can perform blocking operations and notify the main thread with a callback or event when things complete.
So I imagine that it will make limited use of another core for the thread pool, for example if you do a non-blocking file system read this is likely implemented by telling a thread from the thread pool to perform a read and set a callback when it’s done which means that the read could be happening on a different thread/core while the main node.js program is doing something else.
But from a node.js point of view, it’s entirely single threaded and won’t directly use more than one core.