It most certainly is not. A fit person of average build and weight, say 6' and 180 lbs, will need about 2000 - 2500 calories per day to maintain their health and weight - on days that they do no training. Add just a simple 56mi bike ride and you need an additional 2000 calories. Another 400-500 calories if you swim 1.2 miles before biking, and if you run also...well you need to add some more. 4-6K is a good ballpark figure.

If you just putter about while training, or just do one thing per day then you don't need 4-6K. Or if you are merely exercising to lose weight, then the calorie intake would be less. But if you are training to get stronger, 4-6k is in the ballpark.