While it would be too difficult to say for certain if he is or isn’t anorexic from the information you have given, the fact that you are concerned is important enough to warrant some attention.
Perhaps the gentlest way to introduce the idea is by approaching it though a nutritional consultation. Since he is clearly an avid bike rider and he exercises regularly, why don’t you make an appointment as a couple to see a registered dietitian — a nutritionist who can look at your eating habits, make suggestions about calorie and body fat and exercise. In this way you can approach the situation by using a more positive approach rather than saying something is wrong. He may be more inclined to go to a professional if you accompany him, and it is seen as a way to optimize performance. It may also help that the professional isn’t a therapist.
Most registered dietitians would be able to spot the eating patterns fairly quickly and be able to make recommendations from there if they felt there was a concern.