So, that was just a birdsnest coral. Not a whole lot of places to hide in it. But a few days ago I found, what I think was, another aiptasia in the tank. I'm not 100% sure. I saw something with that same color, but much smaller, on the side of a frogspawn (on the stalk/base). When I went to poke at it with something to see what it was, it disappeared back into the coral. I assumed it was aiptasia so I pulled the coral out and superglued all around the area where I saw it. I'm hoping I contained it. However, though I've yet to see any despite keeping a close eye out, I'm assuming there's more.
And, of course, suddenly every LFS is out of peppermint shrimp. I know they're hit or miss with actually eating aiptaisa. But I see it as a "you miss 100% of the shots you don't take -Wayne Gretzky"(-Michael Scott) situation. Maybe I'll pick up some Aiptasia-X to keep on hand in case I spot any more.
And this is my invert-only quarantine tank, so no fish in it, which makes these types of situations a little trickier.