No laughing matter

No one sets out to build a dwarven hold. A hold is simply something just the logical result of dwarves.
Say you and a couple of your dwarf buddies find a nice vein of iron in a mountain no one has any claim to^. You and a couple of buddies grab some pickaxes, trail rations and sleeping mats and get to work. The vein proves so lucrative that you hire some more miners and set up some temporary structures. Fast forward a little, and you've dug so deep that the walk back to the surface is a slog. Most of the areas near the entrance are just featureless corridors and empty caves. Why not knock a few walls down and build some dorms, and storage rooms?
Fast forward a bit more, and you have more space than you need. Now's the time to set up foundries and areas for artisans to improve the value of the goods you bring back from below. Jewelers and stonecarvers and blacksmiths, plus the all the hauling and furnacework that's required. Soon the miners are only a fraction of the mine's population. For every miner, there's one artisan, one person hauling, and one person cooking or cleaning or organising loads of food to be hauled up the mountainside.
Fast forward more, and most of the veins have run dry but it doesn't matter now, the hold has a bustling economy. The halls are decorated with art and wealth, and while little is being mined, the hold can afford to buy raw goods from other mines to fuel their crafts. Some holds fail at this point, as there is not enough to keep the economy running. Some turn to more easily renewable pursuits like magical crafting, and some holds just dwindle until their population better matches the hold's fortunes.
Doren's Hold is in this last stage. There are few mines still operating, but the hold itself is bustling along quite nicely (apart from the occasional abberation attack). The forges burn hot, but they need more raw materials. To achieve this, Doren's Hold is looking to establish a nearby mining outpost to keep themselves supplied. Scouts are sent forth, along with surveyors, diviners and those random nutters that like the open sky.
On the 359th day, Jelk "Chuckles" Bronzefist and more than two dozen of her rangers were investigating a promising mountain range to the south of Dejune. The mountain had a serious roper problem, but that's why Chuckles was there. When the undead and demon attack started up, Chuckles decided their best bet was to head north, and to try and seek refuge in the Calaelen Dominion. Chuckles was actually not aware that Greyton was under attack, but, all things considered, The Great Downward were due for some good luck on this terrible day.
^"No one as any claim to" is a very fuzzy concept. People may have claim to it, but they might be goblins. Or orcs. Or just not paying attention at the exact time.