The part that you're not getting is that the complaint was about the perfectly legal activity of open carry that the complaintant didn't know was legal. There was no allegation of anything that was actually a crime. It would be different if the woman had said "They're waving their guns around, terrorizing people" which is an illegal activity. But no such allegation was made.
The officer stated he asked for ID to ensure the carriers weren't felons, but the Stop and ID law doesn't allow them to do that. They need actual suspicion of a crime under the law. Thus the officer made an illegal demand of a citizen and subsequently made an illegal arrest.
The only way reasonable suspicion could be met is if one of them was overheard saying something like, “I couldn’t get a concealed-carry permit because of my felony conviction. I’m relegated to carrying out in the open. Hope my parole officer never finds out.”