Stacked Deck mechanics

So, until today I thought that Stacked Deck's results were unaffected by anything, meaning wherever you opened them the card chances were the same. Today, while playing with a friend on console, the following happened:

We made a 100+ quantity / rarity Cemetery map, we added a Winded Scarab for extra percentage Divination Cards plus mortal 3 mortal fragments. My friend was after the Brother's Stash card, with for those who do not know it one card that awards 5 Exalted orbs. The card did not drop from the slain monsters, but, my friend had brought with him around 50 Stacked Deck packs. He proceeded to drop all of them to the ground and then picked them up and started opening, long story short the card dropped from those packs.

So I wanted to know, in this league, I personally opened more than 300 Stacked Deck packs, no significant card dropped (I opened them into my hideout), the best I assume was Rain of Chaos. How did that my friend manage to open a Brother's Stash this way? The card is suppose to be a Cemetery exclusive drop, and yet he managed to open a Stacked Deck that contained this card.

Did the dropping them into Cemetery gave them chances to drop as Cemetery cards?
I tried looking in up in the Wiki page but I didn't found any clues, if someone know how this mechanic works and he's willing to spare some info I will appreciate it. Thank you all in advance!

That would be huge exploit if true, wonder if all those MB came from it :)

Stacked decks can drop any card regardless of restrictions. But the cards ARE weighted based on their rarity.

I meant if decks are somehow affected by map's IIQ, either global or card-specific

Need a much larger sample size to see it as anything other than rng.

Stacked Deck uses its own drop table to determine which card it will drop, it doesn't matter where you open it.

"

The card is suppose to be a Cemetery exclusive drop ...

No it's not. Brother's Stash can also drop from The Gambler cards, Stacked Deck cards, and The Void cards, as explained in the wiki.

What you witnessed was a normal Stacked Deck drop, which happened to be in a Cemetery map.

This is RNG mixed with confirmation bias. Stacked decks are not affected by any outside influences like map quant, player rarity, player level, zone level, anything. It's just a flat (weighted) chance to get any card. The fact that you got a Brother's Stash is RNG being on your side, and was not affected by anything you did.

I know and I have read that the Stacked Deck's drops are weight based and purely random, unaffected by any parameters. But still I was extremely surprised when this happened in front of me, it was like my friend knew this would work and indeed worded. What are the chances of doing all that and them, for a mere 50 packs, this card dropped? It's just that the coincidence is huge for me to accept it even if the forums clearly state it's random.

Any possibility the mechanics behind are flawed and indeed stuff like this are able to occur?

You just got lucky.
I've got Brother's Stash from a stacked deck in my hideout before.
And it was a stack of 10.
Should this mean that you get at least 1 Brother's Stash in your hideout for every 10 stacked decks? ofc not, that'd be silly