Insurance companies differ on their definition of a new driver. Even though you have work insurance to drive a truck some companies might not consider this as previous insurance since it was not on a personal vehicle. Or if you only had a commercial driver's license and not a passenger vehicle driver license's until now many companies would consider you a new driver since you do not have a driving history with passenger vehicles.
To find out the reason specific insurance companies term you as a new driver you will need to ask them and also ask how long you will be designated as a new driver. If you want to start auto insurance comparison shopping you can begin right now.