In order to impress her working-class family, the valet tells them that Alfred is the well-known professional championship fighter who happens to have the same name and fights under the professional sobriquet "Battling Butler". From there, the masquerade must be maintained, in public and in private.
To win over her humble family with his working-class roots, the valet fabricates a story that Alfred is a famous professional boxer known as "Battling Butler", and thus, the ruse needs to be maintained both publicly and privately.