It was goblins vs gnomes expansion(GvG)
Here is something from reddit concerning HS. Someone else had asked about what the fiasco was about, and wanted to know what silly stuff happened
"There is a running joke about deck slots. Players have been asking for additional deck slots(more than 9) like since the game was in Beta. The official blizzard response was that more slots would confuse newer players. 9 is an okay number, but if you expiriment alot, and like to save your old designs than it is not nearly enough. You can have like 2 or 3 decks for each class you mostly focus on, 1 or 2 joke decks, a couple decks you are tweaking, and a couple decks you copied online. 9 Slots is not enough.
The amount of people who bought the wrong packs proves that the intelligence of the average player was low enough to be confused by 2 pack options, let alone being able to choose between more than 9 Deck slots"
And a serious response followed:
"That’s not an intelligence issue, it’s a UI design issue. The people who bought the wrong packs included big-name streamers and tournament winners, and it’s much more reasonable to point to failures of the UI than to assume that so many players have the mental capacity of 3-year-olds.
Comparing the UI then to the UI now shows exactly how they got things wrong.
Classic packs were selected by default. Now, the newest expansion is always selected by default.
Classic packs are on top. Now, newer expansions are on top. Notice how in Duelyst, newly edited decks go on top.
The choice between packs took up a sidebar that was a third the size of the giant pictures of packs on purple velvet. Prior to GvG, there was only one pack type, so this sidebar didn’t even exist.
There wasn’t anything that stood out to distinguish GvG packs from Classic packs. The two packs look very different, but HS is a victim of its own stylistic choices and the differences in color schemes and details get lost in all the graphical noise. Now, there’s a somewhat prominent banner over whichever expansion is the newest.
Blizzard’s design for these packs was basically the equivalent of a push door with a handle on it. "
Jokes aside, it was a very big priblem for a ton of players.