Possible Continuity/Cannon Error Regarding Nardole

In The Return of Doctor Mysterio, Nardole says to the Doctor that he (the Doctor) cut him out of hydroflax because he (the Doctor) would be worried that he would be lonely (in the absence of River)

But, we see them meet for the first time in season 10 and the Doctor is surprised to see him, and I think he also claims that River Song sent him to keep a watch on the Doctor.

Is this just a canonical error? Or am I missing something? Plz help r/DoctorWho