When I measure an octave on my CT-S1, it is 162 to 163 mm depending on the octave. The statement that a full size octave = exactly 165 mm is incorrect. There is some acceptable variation from one manufacturer to the next. If you go to two different grand pianos, you will find some variation too. 2 or 3 mm per octave should not cause frequent mistakes. I think that the texture on the keys, the height and depth of the keys, and the key action are all much more likely to impact the number of mistakes compared to a very small difference in width. Lots of information on this topic available here: https://www.mrpianotoday.com/are-piano-keys-same-size/