Public shaming does not equate to an attempt to convert. That’s a separate issue.

You’re also conflating religion with faith practice. You’re assuming they are both of the same religion and that because one is born into a particular faith tradition that they must remain in it in adulthood. This is false. The suggestion of "secular" recognizes that the store patron, if they are a member of a Christian Church, had rejected certain elements of the faith or isn’t actively practicing.

You’ve rejected my examples of other religions. I disagree, but fair enough. How about these:

You don’t see Shakers shaming people for not practicing celibacy, failure to dance ecstatically, or denying the equality of women.

You don’t see the Amish shaming people for using electricity, wearing buttons and zippers, or not bundling.

You don’t see Mormons shaming people for not following plural marriage or not doing missionary work.

You don’t see Catholics shaming people for not worshiping Mary or recognizing saints.

You don’t see Holiness practitioners shaming people for not handling poisonous snakes.

You don’t see Pentecostals shaming people for not speaking in tongues.

You don’t see Unitarian Universalists shaming people for believing in the divinity of Jesus and the Trinity doctrine.

These are all faith traditions of Christianity. There are 10 major sects of Christianity, many with several different cultural faith traditions within them. Every single one of them manage to observe and practice their faith traditions without deliberately making a public spectacle of themselves shaming people who do not follow any religious practice at all, people of a different religion, or even fellow Christians who follow a different faith tradition.

Only Evangelicals and Conservative fundamentalists, as a group, have the hubris and gall to do that. It’s an uncivil behavior they are known for.

There is absolutely no reason other than an obnoxious need to perform one’s perceived spiritual superiority over others to not have quietly excused themselves and gotten another clerk or a manager to service that customer and still maintain their faith observance.

The whole point of the public proclamation and smirk was an effort to shame another as a means of elevating oneself over that person. It was pure ego.