That's just a starting estimate for a moderate intensity ride. Most of my clients are women, they are not doing intervals typically because a lot of them are fairly new to riding or triathlon so the intensity of their rides are often lower. This would be adjusted depending on how they do. I personally shoot for 200 cal per hour myself but I'm 5'7", have a fair bit of lean muscle and exercise at higher intensities. For a more advanced rider with more muscle on them, I'd likely start at 200/hour.

I also recommend having some form of quick food on hand as emergency food in case you start to feel bonky. That extra gel I pack has saved me many a time.