Agree with you. On the presentation of Model X the 90D was called the base model on the big screen.
Here is a quote from my email (I edited with bold):
We’re pleased to confirm that your referrals, along with your Tesla account credits, have earned you the opportunity to purchase a fully loaded Founder Series Model X, which is not available to the public, for the price of a base-level Model X.
I also agree. A P90D is not the base model. But we haven't received official pricing as of yet, so perhaps they will catch the error or re-think it. Don't get me wrong, I'm not trying to look at a gift horse in the mouth. A loaded P90D for the price of a P90D with no options is still very good, but that's not what the terms of the program stated (dare I say 691HP? <running away quickly...>)