I wouldn't say the evasiveness was purposeful. Robert misunderstood something Eliezer said fairly early, taking it as an attack when Eliezer was trying to make a point about normative implications. This probably switched Robert out of curiosity-mode and into adversarial-mode. Things were going fine after Eliezer saw what was happening and dropped the subject. But later, when Robert didn't understand Eliezer's argument, adversarial-mode was active and interpreted it as Eliezer continuing (in Robert's mind) to be a hostile debate partner. I doubt Robert thought he was in trouble; more likely he thought Eliezer was in trouble and was being disingenuous.