These explanations arent great. It doesnt really have much to do with RAAS activation. It has almost everything to do with a phenomenon called the alkaline tide. In chronic vomitting, you would expect Cl- to be low and K= to be low (similar to lab results in someone with bullemia). To compensate for the low Cl-, the stomach has an antiporter which exchanges Cl- for HCO3-. Therefore, Cl- will be replenished in the stomach, while HCO3- will increase in the blood, causing an alkalosis. In alkalotic states, the H+/K+ antiporter will begin to activate, shifting K+ INTO cells (hypokalemia) and increasing pH. RAAS probably plays a role in making the hypokalemia worse but the alkaline tide is more important here.