I spoke with someone in the housing business back then who gave the same explanation. The cost of lumber skyrocketed, which led to an increase in the price for new home construction.
It was not just the increase in lumber.
Everything went up in price:
Labor
concrete
windows
doors
appliances
carpet
flooring
electrical romex and components
rebar
plywood
osb
cabinets
roofing
drywall
basically every component to new home construction
Just this week I was told by a customer in northern Idaho that a big job was delayed because the local concrete companies could not get enough Portland Cement