How does NodeJS work?

Question

Node.js

1. Do I understand correctly that NodeJS asynchrony is achieved by descriptor polling (epoll) for I/O operations?
If the answer to the first question is yes, then:
2. Worker threads are mainly needed only for CPU intensive operations, since even one thread would be enough for epoll ? Even the node developers themselves say: "Workers (threads) are useful for performing CPU-intensive JavaScript operations. They will not help much with I/O-intensive work. ". ?