It's because the flight does not cross a meal time. I think it's 7am 12 noon and 7pm that the flights must cross. Someone can correct those times if I'm wrong. As far as the meals, light means choice of a hot sandwich or dinner sized salad w/protein. Included is a small fruit bowl and a cup of soup. Really a decent amount of food. This is basically for lunch service that crosses noon time.

Hot meal means a choice of two hot entrees, one of them being a sandwich the other, dish-up. It comes with a small salad and a cup of soup. This is for a dinner service that crosses dinner time.

Cold snack plate is for flights of sufficient duration that do not transition meal times. The cold plate is on the small side but it also comes with a fruit bowl, crackers, sometimes cheese (but not usually in my experience, and no I don't snag it for myself) and a packaged cookie like a Milano.

Referencing your examples above, the first flight leaves at 1:10 and gets in around 5:40. The second flight leaves at 2:30 and gets in around 5:00 neither cross the magic hour.

Edit: After thinking about it, cheese is always there but either it's on the plate or it's prepackaged on the side. On the side is rare, on plate, common.