A lesson I learnt came from a fitness guy I watched. He said, missing out one day happens. Shit happens. Missing out 2 days is a choice.
I couldn't go out yesterday cause a storm came through. So I did 2 times what I normally do. I don't know if the effects will pan out, but at least I can say I did not slouch. I am ~3lbs away from my desired weight.
Depending on his goals and where he is double it might or might not be good. You can get overuse injuries. Doing 10 pushups in a day is good. However 100 in a day is likely to lead to injury so you should instead increase your load anytime you are able to do more than 20 pushups in a setting (think one-arm pushups with a weighted vest...)