Coincidence, Dimensional Cross-over, or Crazy Couple?

I teach high school English in Texas. Back in 2010, my husband and I went to the San Antonio Riverwalk for one last getaway before the school year started. We were eating at Joe's Crab Shack when I noticed that a boy in the family we sat next to looked like one of my students from two years prior.  I didn't want to stare long enough to be sure, though, that it was him.  However, a while into the meal, I heard the young girl (who I assumed to be the sister) call this boy "Keenan," which was the name of my student.  I turned quickly now to look at him, and they all looked at me curiously.

"Are you the Coles?"  I asked.  [I have changed their last name.]

"No," they replied.

"Oh, I'm sorry," I said, "I just heard her say Keenan and I taught a Keenan Cole two years ago --"

"Oh," the father cut in, "This is Keenan Cole!"  he said, pointing at the boy.  Keenan smiled quietly, as was characteristic of him.  "This is Keenan Cole," he said again, "But we aren't the Coles." 

So I assumed perhaps this was Keenan's mother and a stepfather, hence the different last names. 

"He's been saying you look like his teacher," the mother said.

"Well, guess what," I said smiling at Keenan, "I am teaching juniors this year, so I might get you again."  He was still just smiling and the sister now had him in a playful headlock. 

"I hope we don't get any bad notes home this year," the mother said. 

I told them that while I didn't remember Keenan being a problem himself, he had been in one of my rowdiest classes, and I had sent a few emails to parents that year. I reviewed some of the names of the more "energetic" boys in Keenan's class, and he nodded in agreement, laughing with me at the memories. 

So that was that and we said goodbye when they left. 

When school started, I did end up with Keenan on my roster.  On the first day of school, I mentioned seeing him on the Riverwalk.  He said nothing until I mentioned it again later, and this time, he said, "That wasn't me."  I questioned him, not just that day, but for several days because he stuck to his story -- he had never been to the Riverwalk this summer.  He even swore to God and he never swore to God, he said. "I was supposed to be at the Riverwalk that week," he did say during one conversation, "But I didn't go. You can ask my mom." Because this was a personal matter and not school-related, I chose to Facebook-message his mom instead of using school email. That is when I saw that she was not the same woman I had seen on the Riverwalk. She replied that they were never in San Antonio this summer. "I work nights, and he was home taking care of his sister." She went on to express some anger at the people who must have been trying to trick me. 

Other people have suggested it was a prank, but believe me when I say that they didn't have time to plot like that. This was all instantaneous conversation. Also, we live over two hours from San Antonio, so it's not like Keenan could have snuck to the Riverwalk and back home while his mom was working. 

My husband is my only witness - he saw the family and heard the conversation. To this day, I cannot explain what happened.