If Steve’s Tony has been listening in, and he isn’t this time because Tony already knows that Steve will win in a fight if it comes to that, especially with Stark’s current level of technology, he might believe that Steve’s lying skills aren’t even coming into play now. He’s mostly omitting, but he’s not saying anything false.

He could also have predicted his younger self’s reaction, which is an arched eyebrow and a smirk.

“Who put you up to this? Pepper? Is this Coulson’s newest way to break the I...oh. That joke is probably too soon. I know he’s been very excited about your updated costume. He scanned in hand drawn sketches. It’s cute. Or creepy. Depends on how you’re swinging I guess.”

This Tony hasn’t met implausible yet. He hasn’t lived through aliens trying to kill him yet. Just people.