The rationale for the move is standard Duquette: after an extra-innings affair that depleted an already-taxed bullpen, the Orioles will be in need of a fresh arm for at least a couple of games. Gausman, having started tonight, wouldn't be needed for four games, so his spot can be used for a reliever for a few days and they can worry about who will make the start then.
Unless he is called back up to replace a DL player, Gausman can't return to the Orioles for ten days. Reporters still at the ballpark indicated that the move did not seem to reflect Gausman's performance, but rather him offering the most flexibility to the team. MASN's Steve Melewski specifically said that he thought Gausman would only miss one MLB start after being optioned.
Here are your minor league pitchers on the 40-man roster: Jake Arrieta, Mike Belfiore, Zach Britton, Dylan Bundy, Jair Jurrjens, Josh Stinson. Belfiore was optioned within the past ten days, so he can't return. Bundy is working his way back from an injury. A failed fifth-starter could sit in the bullpen just in case for a few days. If they aren't needed, they might be candidates to start the next game in Gausman's turn, which is Tuesday the 18th, opposite Justin Verlander.
If the extra arm is needed and neither of those choices are employed, they would just be shuffled off again for an expendable sacrificial lamb starter who can hopefully go five innings.
Melewski also indicated that Gausman could be called back up to replace a player on the paternity leave list, and as fate would have it, Miguel Gonzalez is expected to be going on that list in the very near future when his wife gives birth to their first child. Gonzalez's next start is scheduled for Sunday. Rooting for his wife to go into labor after he pitches next but before Gausman would pitch next would be pretty weird, but being a sports fan is weird. So is life. You are weird. I am weird. Everyone is weird.
If the Orioles want to call up a different player, they would have to move a player to the 60-day DL or DFA someone. There are no 60-day DL candidates.
Even a prized prospect is not exempt from the roster merry-go-round. Gausman will probably not learn much in a single AAA start (if he makes one) and he will probably be back after he makes it, if he doesn't come back sooner. There is no doubt the Orioles need an extra arm for a few games, so we may miss Gausman on Tuesday. That's life in Dan Duquette's world.