Dealerships are profit hungry these days. They are not earning much from car sales so they are trying to make profit other ways.
The warranty book of 11th gen Civic is correct and in compliance with the owner's manual which is the most authentic source of info for the vehicle.
Honda 0W-20 API SP is fully synthetic oil.
Synthentic oils must be changed at 6 months or 8,000 km which ever comes first. It can go up to 10,000 km but honestly you can never meet those (non-severe) conditions.
In case of 11th gen Civic, if the maintainance minder informs you to change oil earlier than the intervals mentioned above, then do it. Don't wait for 8000 km or 6 months mark.