Earlier quoted context omitted.
In the video, he proposes that the printer would have a second pick and place type arm that would be able to install plumbing and electrical systems. He claims that it could be used to do finishing work too, but there are no animations to suggest how that might work.
So, wave a wand and say "a robot will do it". That doesn't count as "A printer that can print a 2500 sq ft house". Even imagine the robot exists: how exactly does it just 'plug in' the plumbinb and electrical systems? Currently it takes a person to scramble all over the house, drilling and fitting and connecting. There is nothing being solved here. Just a blue-sky story about an imaginary printer.
Could you watch the video? He already addresses these issues, and they are clearly researching how to do this. This is just a giant pick-and-place machine working with larger components. They already show that some human effort will be required in the assembly process, but hopefully will be much safer than what is done today.