An Introduction to Multithreading in Node.js

I wonder why node call workers "threads" when they're actually os processes spawned like fork()

   const { isMainThread } = require('worker_threads')
   if (isMainThread) {
       const { Worker } = require('worker_threads')
       const worker = new Worker(__filename, { workerData: {})
   } else {
       const { workerData } = require('worker_threads')
   }