Splitting from Elder Lyons (and stealing technology in the process), Casdin and his fellow warriors were of the opinion that Lyons had "gone native," concerning himself with the troubles of the locals instead of the "greater" mission: the acquisition of technology. Lyons hasn't even bothered to get his giant robot working, let alone continue the search for technology. In Casdin's eyes, the Outcasts are the true Brotherhood of Steel, carrying on the missions of the main West Coast contigent.
According to Elder Owyn Lyons, he was one of the best fighters in the Brotherhood of Steel before he took other Brotherhood members and formed the Outcasts in order to continue the original mission.
If asked about the Outcasts, he will comment on how he fought side by side with Elder Lyons in the scourge of The Pitt. He recalls how the Brotherhood was forced to watch over small towns instead of gathering technology. This ultimately led to the split of the Brotherhood and Protector Casdin becoming the Outcast leader.
*Henry will replace his armor with a set of Enclave power armor but will replace that armor with the Tesla armor but not the helmet, when you trade the armor for supplies in the unmarked quest, The Outcast Collection Agent.