I noticed the "checking ID with a light" thing at LAX this weekend as well. I was in the elite/F line in T4 (AA), and they scrutinized each passenger's ID with a UV light. They looked at mine for maybe 10 seconds, but they took about a full minute to examine his. We both have NY drivers licenses. They barely glanced at the boarding passes.
If this is a new procedure, they aren't following it at JFK. If this is a wonky LAX procedure, I'm sure the TSA blog will clear it right up!
New procedure, just went into effect on Feb 1. *All* passenger IDs are checked with the UV light now, or the magnifying loupe for older IDs without holograms/UV features.
It's possible that the other person had an older NY license, depending on when it was issued some of the security features are different. Also, well-used IDs tend to get worn down some and that can affect how easy it is to see some of the features.