You do not need IIS, Apache, or nginx if you already have node serving requests. Also, depending on your OS, some of those technologies might not be available (ex. if your server is a Linux server, IIS will not be available).
"What are you running your app on?" That is a somewhat vague question. Possible responses to that question would include:
- Windows/Linux
- Node
- The internet
Maybe the weird looks are coming from those who do not know what node is.