Kostya isn't writing about the cunning of the dwarves, but about his own absent-mindedness – he just needed to place a 1 on the cell above.
It was funny, of course :D, a clever move by the dwarf... in general, going there is 95% dangerous, as any extra morale loss leads to defeat, especially on the grass.
I don't like the conditional mood, but if the dwarves had been taken, the 5000 gold would have been used to buy a second hero with 6 elves, and the growth would have been bought in the form of 6 dendroids and 7 elves, centaurs, and dwarves. With all of this, I would have taken a level 2 fortress and a chest with 10k experience, and it would have given me some chances to do something in a long game.