You missed the point -- spring traps would NOT be legal.
It is pointless to speculate what Texas law or other State laws would be, you don't know. I am not missing any point. Your point is that an Iowa case ruled that according to Iowa law people in Iowa can never use lethal force for the sole purpose of defending property. You also claim this applies in all States. Your claim has been proven false by counterexample. In Texas people have and still can used lethal force legally for the sole purpose of protecting property in certain situations.