Why do good people play dumb and sign with you?

A good man pretends to be deaf and gesticulates with you, probably because he thinks you are deaf.

On the way, in order to avoid embarrassing things, a good-hearted person plays dumb and gestures with you, because he may think you are deaf.

Sign language is a language that uses gestures, body movements, facial expressions, etc. You don't need pronunciation to express your meaning. The main users and users are people with hearing or speech impairment. For the general public, sign language is not universal, but it is a very common way of communication among deaf people.