Roxas had been thinking of Riku when he mentioned the body snatching, though he mostly knew of that from getting his ass handed to him and from eavesdropping on Sora later on. That was a little beside the point and he really didn't have any details beyond that, though he wondered if those details might help them come to some answers.

It was obvious the mention had made Sora uncomfortable, so Roxas didn't go into anymore detail on it... at least, he didn't name names, though he gave Sora a meaningful look as he spoke, "I exist partly because of that. Because that Heartless dropped a hint about a Keyblade that unlocks hearts and left that Keyblade lying around after he was beaten in a fight."

If Sora didn't want to mention that Riku was specifically the one who had been possessed, Roxas wouldn't either. That part wasn't the important detail anyway. The behavior of the Heartless was.