Sorry, I don't know the app you're using, and I couldn't find it.
I was talking about the built in Calendar app that comes with your iPhone.
In general:
When you create an event for one account, it will sync through that account, and not another one. An event set up in iCloud, will sync via iCloud, and appear in iCloud, and nowhere else. It will sync to other devices with the same iCloud calendar, not to a different calendar.
What you see depends on which calendar you chose. If the app is set up to show the iCloud calendar, it will show iCloud calendar events. If it's set up to show a different calendar, but not iCloud, the iCloud calendar will not be visible. Usually, you should be able to see all of your calendars at the same time.
iCloud as default calendar means when you create an event, it will be set up for iCloud automatically.