There isn't always a clear distinction between mercenaries and soldiers. Both perform military service and expect payment in return. Most (American) soldiers don't see pay as the main factor for enlistment, but some do. In many countries and throughout history, however, soldiers have served and do serve mainly for pay. Likewise, many mercenaries have had other reasons for serving. For example, the many foreigners in Rhodesian service during their war received the same pay and benefits as Rhodesian soldiers, minus some rights of citizens. They were motivated mainly by ideology, like most of today's American soldiers.
So yeah, Form was probably just using the term for political reasons, but I just want to point out that the line between merc and soldier is blurrier than many think.