Skin shard re-rolls are (probably) not random

So here's what happened: As of Tuesday night, I owned every skin in the game you can get with money at this point (so no old Victorious skins, PAX skins, not every Hextech skin, or anything like that, but I did own all legacy skins that have gone on sale in the store). I wanted to get Prestige K/DA Kai'Sa but didn't have enough Worlds tokens, so I bought a bundle of K/DA orbs that came with tokens. I opened all the K/DA orbs and had a ton of skin shards for skins I already own, and I was like, what would happen if I re-roll them but there's nothing left to roll into? What happened is that I got every single Hextech skin (minus Annie which I already owned) and also Prestige K/DA Kai'Sa. Once those skins were unlocked, my next re-roll resulted in a skin permanent for a skin I already own, so I believe I hit the end of possible re-rolls (so no Victorious skins or other limited skins like that).

While I am psyched to have all the Hextech skins now (I open so many chests and have only gotten a total of 18 gemstones so it was such a slog), I am kind of annoyed because it seems like too much of a coincidence that my "random" skin shard re-rolls resulted in 10 Hextech skins in a row at the very end of my collection (random note: Prestige K/DA Kai'Sa showed up as a Hextech skin). I'd like to hear from others to see if anyone has received Hextech skins when they re-roll shards. I think it's a bit disingenuous of Riot to claim skin shard re-rolls will result in a random unowned champion shard if, as I hypothesize, all the most rare skins only get re-rolled when there is nothing else available.

Related: Riot, please release a Whale Nami skin to reward those of us who are obsessed with buying skins. XD