"Ah. My mistake." Sephiroth smirks a bit. "Then just now...you weren't inviting me to...?" Genesis is free to interpret that as he will, but in context, if he's able to focus enough to replay their conversation in his head...he might realize that Sephiroth actually took his remark as a suggestion to do his worst. The mere fact that he didn't immediately do so - long enough for this clarifying moment to occur - and that he actually double-checked to make sure it was what Genesis wanted...it speaks worlds of his dedication to Genesis and following his instructions.