Yes it's a big breakfast but if a normal diet is 2000-2500 calories per day, 820 for 1 meal doesn't seem that weird.
The basal metabolic rate for a 30 year old male who is 5'10" and 160lbs is 1700 calories. So that's how many calories they burn by merely existing and breathing and being warmblooded. Your argument is that someone working from home only uses a max of an extra 100 calories a day over BMR? Doubtful.
If you lift weights or do other strenuous exercise 3-4k calories a day is needed. The trick with calories is just to not consume more than you are using if you don't want to gain weight.