As a personal agnostic raised Catholic; I feel the need to address the mob mindset, so if you want an actual answer: the term pro-life isn't a dogmatic Christian term. Christians believe that it's okay to kill in defense of the innocent, for example (in some cases, even if there's risk of collateral). That's Catholic dogma. If Noah and his family were the only innocent people left on Earth, and their exitence threatened the existence of the innocent, then it wouldn't be against the Christian God's nature to kill them. Also worth mentioning that the first books in the Bible are generally regarded as poetic history, with probable exaggerations in terms of scale.

"Pro-life" is a modern, semantically unexact term that is usually used to indicate that they believe an unborn baby is an innocent human being that shouldn't be killed. That's all there is to it.

I'm not getting into a debate about the veracity of religions; but I think it's silly to be moved by the interaction of two people on the street instead of by reasoned debates.