I don't know the answer for sure, but since this may not get any replies I'll tell you what I think.
All the chess.com bots are komodo, just using different settings, so if he wanted to play mittens vs mittens but one of them with riskier openings he could just show a komodo vs komodo match where one copies all of mitten's sittings, and the other copies all but one setting.
Another way might be to start the game from a certain position, or take back moves until the engine plays something more risky.
In any of these methods he can hide what he did in the editing, so that for users it just looks like mittens vs mittens.
AFAIK there is no way to tell a bot to play risky or safe on the normal chess.com interface.
In GothamChess mittens vs mittens he said he sugested for the computer to play a more risky opening, how did he do that?