He’s right about the hydrophobic and hydrophilic aspects of detergent molecules, but the part about the alkali metal (eg sodium, potassium, etc.) is incorrect. It forms an ionic bond with the acid part of the fatty acid, and so it dissociates when the soap mixes with water. The negatively charged carboxyl group interacts with the water, and it’s covalently bonded to the hydrophobic hydrocarbon chain. The sodium, potassium, whatever just goes into solution and doesn’t act as a detergent itself.