So are we supposed to consider Kid in a Fridge canon considering that it completely goes against established Ghoul lore?

Probably not.

But maybe, maybe, ghouls or certain types of ghouls are capable of a type of https://en.wikipedia.org/wiki/Cryptobiosis under extreme conditions. The kid surviving could be a result of him going into such a state for those 200 years.

That would be a better explanation at least than "Ghouls don't need any kind of sustenance to survive." Which I personally think is ridiculous.

That wouldn't be a bad solution. I wish there was some way to contact Bethesda on the issue but sadly that's not really an option

It's certainly not the only lore they screwed up in the series

It's a stupid quest that makes no sense and can comfortably be ignored. Pete Hines effectively admitted he didn't give a [censored] when it was brought up and neither should anyone else.

Basically equate it to meeting King Arthur and his power armored knights or alien crash ships with pictures of Elvis

It could also be that a Ghoul only needs a small amount of radiation to sustain important bodily functions. With Rad-Storms it wouldn't be too hard to imagine a Ghoul could live a long time alone on that, since Rad-Storms seem pretty common at least four days a week. And considering we can live a long time without food, maybe that's sufficient enough to keep a Ghoul alive without water which is pretty important.

In a game where dead ghouls can literally be brought back to life via radiation, I don't understand why some people seems to have such a hard time grasping that radiation = ghouls live.

That's possible. Though if that is the case then Bethesda really needs to clarify that.

This is essentially my feeling on it right now tbh.