That’s what I thought as well. A witness, or a defendant, can be called up to the stand, answer some questions, and to others invoke his right not to self-incriminate. Bravo to you.
If a defendant is asked “Do you intend to invoke the 5th amendment?” and he answers “Yes”, he’s waived his priviledge. Remember Mark Fuhrman? F. Lee Bailey asked him “Do you intend to claim your fifth amendment priviledge to every question asked? Mark said “On the advice of council.....”