The owner's handbook and service document that accompanied your car from the factory are correct. The first service, therefore, should have been at 12 months or, if you had racked up 20,000 miles before then, at that point.Just noticed however that the Service book clearly states 12 months or 20k miles
(Some) dealers look to cash in on what they perceive is an opportunity to charge the customer for a major service on occasions when an inspection is all that is required. The first service is crucial in setting the trend but for low-mileage users, say 8,000 - 10,000 miles at 12 months (or less), the first service would only be an inspection and the major service would be performed at 24 months. To avoid any problem with warranty, it would be wise to ensure that you do not exceed the 20,000 miles between oil/filter changes so you need to bear that in mind if you don't fit neatly into the low-mileage criteria.
Ignore any 'experts' (and dealers) who would have you believe that the oil and filter should be changed every year or every X-thousand miles, just for 'peace of mind'......or, 'if it were me'. They are still thinking in 1950s mode - these modern fully-synthetic lubricants are amazingly robust and can cope with high mileages and extreme temperatures incredibly well. KIA, and many other manufacturers, are very confident in their service intervals now that fully-synthetic oil has proved itself time and again in the most challenging conditions so there is no question of 20,000 miles being too long an interval between oil changes.