Frankly Ianto is just as disappointed about the clothing situation but since they technically don't really know each other he thinks it's probably for the best. He finds this younger version of Jack far too interesting for his own good right now and he would rather avoid distractions until he can learn a bit more about him and whether or not he's dangerous like this.
The new name jolts him back to his senses and does a good job of reminding him just how little he knows about Jack right now. "I'm guessing you must have a lot of questions." He does his best at a reassuring smile as he nods for him to follow him to the kitchen.