I think there is some behind the scenes prompting from claude code for plan vs build mode, you can even see the agent reference that in it's thought trace. Basically I think the system is saying "if in plan mode, continue planning and asking questions, when in build mode, start implementing the plan" and it looks to me(?) like the user switched from plan to build mode and then sent "no".

From our perspective it's very funny, from the agents perspective maybe very confusing.