Did you mean to ask the following? “Is not the mean for 4, 5, 6, 6.5, 7, 9 = 37.5/6=6.25, which is equal to the median?” If that was your question, then yes in this case the mean and median are equal which is the condition given in statement 2, and our value for median is 6.25. However, if we choose the list to be 4, 5, 6, 7, 8, 9, then also we satisfy statement 2, however now we get a different value for the median, 6.5 in this case. That is why statement 2 is not sufficient.

Baten says

Is not the mean for 4, 5, 6, 6.5, 7, 9 = 37.5/6=6.25, which is equal to the mean?

GMAT Quantum says

Did you mean to ask the following? “Is not the mean for 4, 5, 6, 6.5, 7, 9 = 37.5/6=6.25, which is equal to the median?” If that was your question, then yes in this case the mean and median are equal which is the condition given in statement 2, and our value for median is 6.25. However, if we choose the list to be 4, 5, 6, 7, 8, 9, then also we satisfy statement 2, however now we get a different value for the median, 6.5 in this case. That is why statement 2 is not sufficient.