A few more points- A crack in a carbon frame is different in look then a metal frame. carbon frames tend to have ragged failures as the layers and fibers delam and break. The photo makes me think of something that got picked up by the tire and swept past the yoke. If it were a crack it would break through a brushed touch up job. So dab a little paint on it and see what happens over time. I doubt that temp differences were to blame. Bike paint is pretty flexible. Andy.