If a creep is going to do something to one kid, he's going to do it to more. At least, that's how it's worked every time Spike's run into them. So even if Frank did ask, Spike couldn't be sure if Kavinsky was the only victim. Spike checks the clip when Frank paused at the door.

"I'm going in." He says, stating a fact, no judgment. "You do what you want." With that, he plants a kick on the door by the door knob, busting it open.