They ended up limiting it to one question and I was actually fascinated by the Herdazian one. I asked and he said that they (humans and parshendi/aimians) can interbreed because they were made by the same person, or rather that they were made with the same intent, that they were made that way on purpose. They don't have a common heritage or anything though.
And no, I didn't think to record it! Dang, I should have thought it out a bit better. It was a brief event, he read for about 20 minutes, did less than 10 minutes of Q&A that focused just on writing techniques, and about 40 people were at the signing part of the event, mostly just casual fans from what I could tell.