Several things are happening at once, and they're all unusual enough that Loki is taking a few seconds to process them all. First, it's exceedingly weird for a summoning circle to pull two people in. Second, the entity sharing his space appears to be a teenager--though, perhaps not one who is currently alive.

"More than a little inconsiderate," he agrees with the ghostly youth, looking at him as if he's never seen anything like him before.

Third: their summoner not only recognizes the boy but seems annoyed to see him. From the shop? "I see you two have a history. I would hate to interfere with whatever discussion you're about to have. I could just see myself out?"

He knows better. Seems like Loki himself was the real target here, and while he's no hero, he's disinclined to just leave some kid in the lurch, even if said kid seems remarkably calm about all this.

"Although, actually, I'm curious to hear you out, now," he says to the wizard. "I'm not sure whether you're exceptionally powerful or exceptionally incompetent, having dragged two people into one spell."