Does it mean he knows about Yeonjo plotting against him? I'm confused

He had his suspicions which was enough for his advisor to urge him to kill Yeonjo. But instead he chose the route of eliminating any of the most likely candidates Yeonjo would conspire with against him, in order to keep Yeonjo innocent, so to speak.

Oh that's why! He's so smart. I wonder what Yeonjo will do next. He's very stubborn so I'm sure he's go all the way with his plan. He will probably fail since the story is still long apparently. Very intriguing!

Thank you