"i do not know what the security point at the other end of the terminal was doing, but it had a much longer line. Has anyone else had this happen? Any light you can shed?"
I had a similar experience in Atlanta in May 2016. There was some issue at the airport (I don't remember exactly what) that was expected to slow security dramatically. It was such a big deal that it not only made the local news, but I got a text from Delta warning me to get to the airport early. So, even though my flight was domestic, I pretended it was international and got to the airport over 3 hours early. Once there, I found there were multiple security lines, and I went away from the center one to the one on the far side, which had only two people in it. And, that line didn't use the millimeter scanner, but just a metal detector. I don't think I've ever been through security so fast, even before 9-11-2001. I was so early I was able to make an earlier flight (the $50 change fee was worth it to avoid a 2 hour wait).
Less drastically, leaving Montreal for the US this past July, the lines for US pre-clearance were so short, I was sure I was in the wrong place or skipping steps. But I wasn't - for whatever reason, that part of the process was just unusually fast.
So, you just never know. But I'm fond of the saying that "at airports, you can either be stressed or bored; choose bored."