Ah, oops.  I was kind of still stuck on his appearance in Arrow so naturally given her friendship with Artemis, who I think should have made an appearance in the show long ago but that's just me, M'gann only knows what Artemis told her as Ollie's sidekick.  Also this is a few hours after their respective battles, so Felicity may have had more than enough time to figure all this out, but again that's just my opinion.