He lets the statement settle. There is an idiom about letting sleeping dogs lie; best to allow that.

But Seto continues with an unexpected affirmation. It's uncomfortable, hearing support for Sigma when Siebren tries so hard to keep them separate, if only in his mind, but...Seto does not know, and Siebren had offered his services. Seto is working with the context he has, and Siebren can take Seto's words as the compliment they are intended to be. "I am unworried about their revulsion - merely their curiosity. But thank you." He sighs. "And...yes, it is, and often the only way to correct those assumptions is with the truth." A truth he is unwilling to divulge fully, regardless of mutual understanding. "Better to control the narrative from the beginning."