First, I seem to have missed (or at least forgotten about) the creation of effective-altruism.com, so thanks for the link!
Second, is it clear to others who the "us" is in the first sentence? Did the anonymous philanthropist ask their question of Nick Beckstead and Carl Shulman in particular, or effective-altruism.com as a whole? (This is perhaps not a super-important question, but I'm just trying to get a more accurate picture of how effective-altruism.com operates and how others interact with the group.)
Cari Tuna's discussion in the comments with Carl seems to suggest that the answer to my question is that Nick and Carl were asked directly were speaking for themselves.
A philanthropist who will remain anonymous recently asked us about what we would do if we didn’t face financial constraints. We gave a detailed answer that we thought we might as well share with others, who may also find our perspective interesting. We gave the answer largely in hope of creating some interest in our way of thinking about philanthropy and some of the causes that we find interesting for further investigation, and because we thought the answer would be fruitful for conversation.