When you told people you were going to have a kid did you get into the intricacies of the decision-making process?

Yes, what else do you talk about when discussing the prospect of having children? It was a pretty big deal to me and not a very difficult conversation to have.

Do you think there’s any chance that perhaps the guy who found out that he and his wife were unable to make their own babies had actual in-depth conversations with his wife about whether or not they wanted to adopt or go childless, and opted to tell his coworker they would just adopt instead of getting into the intricacies of those conversations?

Possibly.

Is it possible he shrugged and said it off-hand because talking about the need to adopt a child instead of making one on their own is painful?

Possibly. Different people handle it differently but I imagine if the man and woman in OP were to be asked the same question I would hear a more considered answer.