Mr. Smith felt uneasy because Reina answered questions hesitantly and seemed to be hiding things. The man actually felt that Kenzo had told all the events that happened in the past and made Reina doubt Mr and Mrs Smith. This made Mr. Smith inevitably have to plan something so that Reina could return to being used as a tool to make Kenzo think a thousand times over to retaliate.
"If it's like this, I must come up with a new plan to defeat Kenzo. Reina must be suspicious of me, so I have to use Reina to destroy Kenzo instead."