David Kimura PRO said about 7 years ago on FullCalendar Events and Scheduling :

The visitor view is just a simple controller and has an action. Within there is a DIV which contains the ID calendar which is where I'm displaying the calendar. You would place the calendar div where ever appropriate for your application.

For the requests responding as HTML instead of JSON, this could be how you're requesting the data. I'm using format: :json which will make a call to get the json data by default. I didn't do anything special in creating the events controller/model. Check your application logs to see how it is being handled. You might get some hints there. 

For the JSON list of events in the jQuery, I'm calling the url /events.json which would be the same in Ruby as calling events_path(format: :json).

Hope this helps.