I'm a Spanish person, living abroad and with a penchant for cooking, and I was too very gratefully surprised by Kenji's Spanish tortilla video. Also by his other Spanish recipes such as Gazpacho[1] or Paella[2].
It's not that they are very orthodox recipes, cut and paste from a traditional recipe cookbook, but instead very good adaptations of them, taking into account ingredients availability and different contexts.
I can't really tell about other cousines, but judging how he cooks Spanish food I'd say he knows what he's talking about.
Add to that that he seems like a very decent and empathetic person and I'd say he's someone you want to listen to if you are looking for cooking advice.