Correct. The "Companies of Iron" are a selection of units and solos without a Warcaster/Warlock to lead them. It's a new League to fill the gap from the ending of the last league to the new league that will be starting after Lock and Load.
It's a short league- but no details how long that means, or when it will start. "Soon".
Other details: You will be able to make a platoon of whatever models you want, or you can use the "Companies of Iron"- select units and solos that grant special bonuses to your platoon. As the League progresses, the platoons will change/grow and new Companies of Iron will be added.
Pretty cool stuff!