Bearing in mind that your meter can operate within a tolerance of + or - 20% a rise of 1.7 mmol/L over two readings is par for the course especially given a small time lapse, for example a true reading of 5 mmol/L could read anywhere from as little as 4 mmol/L to as much as 6 mmol/L.
Then take into account the fact that your levels may have been rising anyway, or rising due to your activity over that half an hour between tests could have pushed your bg level up too. Even stressing about your levels could easily have raised them by that much and testing before and after a cup of tea does seem to me to be just a little excessive.
I wouldnt have thought that 2 x sweeteners and a dash of evap milk would move my levels much at all and I certainly wouldnt waste 2 test strips to find out.