I saw a comment on reddit the other day, which I don't remember exactly, but it said (paraphrasing):
"In the morning (when waking up after a night's sleep), your <something> reserves are depleted so exercising before you eat will burn fat (no, you won't burn muscle)."
It seems to me that the commenter knew about this effect just fine.
This comment was also made here on HN not long ago (maybe that's where you read it). I believe someone also stated that it's not good for your back to exercise too soon after waking.
I believe your "<something>" is glycogen. The basic idea being that if you have no glycogen to burn, you'll burn fat.
I am 99% sure that they did say glycogen. It was glyco-something, anyway. It might have been on HN, although I think I remember fittit. Regardless, that's not important.
Also, it's probably true that it's not very good to exercise after waking, but nobody said you have to exercise after waking, just that you have to do it before eating breakfast :)
"In the morning (when waking up after a night's sleep), your <something> reserves are depleted so exercising before you eat will burn fat (no, you won't burn muscle)."
It seems to me that the commenter knew about this effect just fine.