Market appreciation = income??? HELLO. McFly??? And they harvested their new-found paper equity.
My guess was that the author was alluding to the husband's job as a lumber salesman. Strong housing market = strong lumber demand = good commissions = good family income.
But one wonders what the stay-at-home Mom was doing while they paid someone big money to work on their backyard. Why didn't they save the cash and have Mom push the dirt and mulch around? Would have taken longer but cost a lot less.