Alright, if you want to be pedantic, 145 cranks did have higher output, but according to statistical tests, it is not clear that the difference is significant (ie that it was not the product of random variation). It is true that the null hypothesis (there is no difference between 145 and 170) is not disconfirmed, but it is not true that the tests showed no difference.

To say the difference is not statistically significant does not mean they are the same, it means that the difference could be random chance. Could be random chance does not mean is random chance. But you are right, the only clear conclusion is that 145mm and 170mm cranks produce more power than 120 and 220mm cranks.