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.
Link