Barirah's husband was a slave, so the Messenger of Allah ﷺ gave her the choice, and she chose herself. Had he been a free man, he would not have given her the choice.
حدثنا علي بن حجر أخبرنا جرير بن عبد الحميد عن هشام بن عروة عن أبيه
كان زوج بريرة عبدا فخيرها رسول الله ﷺ فاختارت نفسها ولو كان حرا لم يخيرها
Muslim also narrated it in "Emancipation," chapter "Explanation that the right of inheritance (wala) belongs to the one who freed the slave," hadith 9/1504, from the hadith of Jareer bin Abdul-Hameed with the same chain.