They are indeed despicable. Not referring specifically to Christians or any other religious group, but people who threaten strangers with damnation for their choice of reading matter, especially ones who involve children in such medieval practices.

It seems unlikely (though not impossible) that they were responding to the specific book you were perusing. I suspect they were looking for opportunities to enact their little drama as many times as possible with anyone they could isolate and surround.

Whether they actually believed they could save your soul by sharing the 10 Commandments--hardly a persuasive argument for any religion--that seems equally doubtful. The aggression and intimidation were the point. They are at war with the thinking world.