I think it may have had its roots in the era when people that were trying to lose weight were persuaded not to eat late in to the evening; not that there was or is anything inherently wrong in doing so, just that this then cut their overall daily calorific intake without them realising that was occurring but then we got the spin-off about calories turning to fat overnight; the later you ate the more of a problem it would be etc.
I've eaten really big meals about 15 mins before bed, which isn't great for digestion in the long run if done for a long time, but it never reflected in my weight in any shape of fat gain. If people are doing exercise, or moving about sufficiently, to use what they take in, then the theory is that they should balance out.
I have to add that the few meals I have had very late into the evening (11pm onwards) have been very calorific and fat laden.
36.5 kg /80.3 lb Middle-Finger DL (right hand)...