I find this story a little confusing. What were people using as a second ID?

I don't think most people have two forms of ID; most folks just have a driver's license (or state ID). Some people might have a passport or passport card, but lots of folks don't have one or don't carry it unless they are traveling internationally. Military personnel would have military ID, but that's a pretty small minority.

International visitors to the US would be carrying a passport, of course, but any other ID they'd be carrying would presumably be from their home country. In most cases that wouldn't be in English and might not even include any text that could even be compared to the name on an English language boarding pass (a Japanese or Russian ID, for example).