It hadn't been in his intention to lure Nikolas into what felt like safe conversation before springing hard questions like that on him. It just happened that way and he wasn't all that concerned with being artful about it.
The turn in conversation was swift and unexpected, but Roger easily moved with the change. If this had been about anyone but Lucy, he might have taken his time and gotten to know Nikolas a little better. But he cared about the younger Ravenclaw too much to make sure Nikolas didn't feel uncomfortable with his line of questioning.
As a matter of fact, the more uncomfortable he was, the better. "They find them extreme, yet, they don't want you marrying outside of the good ol' old and pure, right?" Roger held Nikolas' gaze for a moment, before shooting Lucy an apologetic look. He fully knew that she had told him about that in confidence.