The commands will trigger a webhook call to your server, where the actual deployment/testing/whatever command you need takes place.
You're basically deploying a thing that'll send http requests to another server which then executes specific tasks. So you've essentially replaced hubot with a web application on the end users servers.
What is the difference?
The end user still needs to run something on their servers to actually do anything for their custom commands, which is essentially what hubot scripts do, which is what my book is teaching people about.