That is the most often quoted stat to me when lefties try to claim the intellectual high ground. They quote me percentages of college professors who are democrats.
You have probably done it in the past yourself.
I haven't that I can remember. But it is true.
It's simple really. Most educators are more liberal minded simply because the nature of education is the process of opening minds over a broad range of subjects.
It goes without saying that liberals tend to be more open minded in general. It stands to reason then that those with higher levels of education tend to also be more liberal as well.