No problem, I needed the data as well.
- The USD value was pulled from the coinmarketcap historical pricing by date.
- The USD field actually uses the USD value of SBD for each date, it doesn't pretend they're $1 USD.
There are CSV/JS files for each currency in the historical folder of the project:
https://github.com/aaroncox/steemdata-reward-history/tree/master/historical
Those are the values it's using.
RE: Steem Rewards History CSV Exporter (via SteemData.com)