J10

Hi, I am looking for a used 2011 Qashqai, today I had a test drive and since I am new to diesel engines I am not sure if it is normal or not to see smoke from the oil filler cap? I know that normally it means that oil have slipped into the rings but on a diesel engine it might be a different story.. The Qashqai has 47000 miles on it and I had another test drive and it did the same, but the other qashqai had smoke from the filler cap even when it was still cold. Is it normal for a 2011 qashqai?