Density

[Rob Nob]

They are comparing the entire City limits of Portland to a similar size bite of Houston that is centered around their down town?
So Portland City limits includes large swaths that are just the Airport, Shipping Terminals, the Columbia River, Willamette River, Ross Island, Oaks Bottom, Smith and Bybee Wetlands, Delta Park, Forest Park, Washington Park, Tryon Creek Park, Powell and Kelly Butte Park? Pretty low housing density there!
Obviously most of Houston's sprawl occurs outside of the 610 loop. This is an apples to oranges comparison. It's pretty ridiculous, though I do agree Portland could relax height limits and Design Review.