Just want to reiterate as a lot of people share this confusion...

A Punjabi can be Hindu, Sikh, Muslim, Christian, Atheist, or any other faith.
A Sikh may be Punjabi. A Sikh may not be Punjabi.
A Hindu may be Punjabi. A Hindu may not be Punjabi.

You get the drift.

`Punjab` is a region and `Punjabi` refers to those that have heritage from the people of Punjab. `Sikhism` is a religion and `Sikh` is a reference to someone that follows Sikhism.