That’s not being a pro choice advocate. He only said that he wouldn’t change the laws on the books and that government shouldn’t interfere. It’s like say filling out a survey saying that government should not interfere in a woman’s decision. You will not find him claiming to be pro choice.
But you should watch the rest of that debate too. Democrats were portraying him as a right wing religious zealot who was hiding his true views.
In those 5 minutes he defended parental notification which is NOT a pro choice position.