The article isn't very well written, but it does raise an interesting question. However, this question requires a clear definition of what is meant by liberal, which is a non trivial matter:
http://www.theatlantic.com/politics/archive/2014/02/the-orig...My to cents:
Let's start by defining "liberal" as those who hold the belief that the current Trend in social, economic or political developments will result in them having a better life. The opposite of that is the quintessential "conservative" adagio that "things are getting worse and worse". What exactly constitutes that trend is up for debate, but I think a precise definition isn't essential for this argument.
Since the percentage of the population that is highly educated is increasing (for whatever definition of "highly"), we can infer that access to education isn't only hereditary. That is, there are some of us who are now highly educated but who's parents were not (yes, it still is mostly hereditary, and almost for sure we will inherit that to our children). This, in turn, results in better standards of living for us than for our parents. So, locally, the trend, seems for us to be moving in the right direction. We vote for continuing this trend of more education for more people, of more access to healthcare for more people, and so on, because if it weren't for that trend we'd be struggling like our parents did.
Compound to that the rich-get-richer phenomena, and then our children will probably keep benefiting from this, so they will most likely also be "liberal". Only when a social revolution removes our now-hereditary privileges will we turn into "conservatives".