Pure RNG.  Personally I start top left and just snake back and forth. 

Exactly what I do.  IIRC, the cards a randomized between every flip, so it doesn't matter which order you flip them in at all.

Oh really?  I just assumed it was randomly set at the start. 

Fairly sure that I heard a CC say that, but that doesn't necessarily make it correct. 

A CC spreading incorrect info?!  Surely that would not happen. 

I once messaged my clan mates if they were getting the same result as me when they flipped a card in the same position e.g. top left corner. Nope. They were all different for them. Also, the only time I completed a Deck of Fate Event (Hilvi) the last fragment was under the last card I turned which suggests to me that an algorithm keeps track of what we flip and, ahem, adjusts, accordingly. Also, I suspect the same goes for pulling shards as I keep getting duplicates of legacy champions and hardly any of the newer champions, which makes it very hard to compete in the arenas.