Not "normal", but not unheard of. Definitely sounds as if he's toxic/ has a lot of released toxins in his system. Even if the Epsom Salts had him running, they basically just clear out the center taking a lot of water with them.
Would he do another flush? This time, try to make sure he eats lowfat/no fat and lightly the day before the flush - salads, vegetables, and fruits (bananas are especially filling.) Most breads are made with fat/oil, so may want to keep that in mind. The day of the flush, maybe try a saltwater flush first thing in the morning, before eating or drinking anything else. Then, again, eat very lightly (NO fats or oils!) or even just juice fast until time to stop eating for the day.
Basically, he wants his colon to be as clean as possible to allow the gunk and 'stones' a fast track OUT. With that in mind, as distasteful as some may find the idea, an enema can be extremely helpful, especially the night before a flush day and/or also towards the evening the day after the flush. Really helps get out those last lingering 'stones' and gunk that otherwise might get plastered back against the sides of the colon and sit there releasing toxins back into his system.
Has he started colon cleansing? A clean colon is every bit as important as a clean liver!
Good luck to you both and hope he feels better soon!