simple dc circuit question
You are using superposition to solve a circuit by solving each source separately, then adding the results. When you solve the circuit for a given source, you have to remove each OTHER source from the circuit. For a current source, you do this by turning it into an OPEN circuit (i.e. no wire); for a voltage source you do this by turning it into a SHORT circuit (i.e. a wire).

So in this circuit, WHEN you are solving the circuit for the CURRENT source, you turn the voltage source into a wire. Then, since the 1k resistor is in parallel with a zero-ohm wire, it has no effect FOR THAT PART of the solution (when solving the current source.) So you can remove it for that purpose only.

For the OTHER part of the solution, when you are solving the circuit for the VOLTAGE source, with the current source removed, the 1k resistor will carry current and can NOT be removed.

Does that help?