Steve was not a stupid person, and after Rocky Horror he would probably be more inclined to ask Tony questions. (Questions like 'what is involved?' and 'will people wear pants?') This once, however, he had absolutely no cause for doubt, and so he accepted without further inquiry.
"Okay. When you're bipedal and feeling better, I'll get your ticket. As a get-well gesture."
Well. Everyone had to learn to question somehow, right?