He’s not right, because big cities exist in all states Montana is a red state yet it still elects Democrats and as a result Montana is a purple state. Same is true for Texas, and Colorado and many of the other fly over states.
True for NH as well. The state government is currently under republican control in all branches, but yet elects dems for federal positions.
In that case, I do have to agree that cities are the cause of it. The cities here have enough population to overwhelm the republican vote to get in republican House and Senate reps. NH has a plethora of small towns and many districts at the state level.