It’s the same thing every cycle. These are my first 4 set items:
This has to be a joke. What is up with Pebble’s? It’s not even like I am playing Acolyte.
My first two uniques were also BOTH Bee Gloves. The weight of these items are too damn high in the loot table. Give us more variety!
My fist unique was not that. 
What was your first non-quest reward unique?
Dropping Pebble’s first shouldn’t be surprising. Item level affects the possible drops and Pebblee’s is the lowest item level set, so it’s the first one that has a chance to drop.
Although Last Bear’s is just one level higher, but for quite some time those are the only two sets that can drop in the campaign, so it’s not too surprising that it happened to you.
It’s just like when you start a new character in D3. The loot pool at low lvl is VERY small