There are tons of activists in many different fields, and there's nothing about being a computer programmer that makes you more likely to be an activist. Just because this guy cited a couple of activists who were also computer programmers is just not support enough -- if he really wanted a balanced review, he would have talked about any activists in any other fields as well for comparison.
The reason it was easy for him to make this connection between digital rights activism and programmers is because it's easy to find activists within a field they work in. So if you're talking about digital rights and internet openness, of course the champions of this are going to be people who work with computers for a living.
If you look at something else like politics, or civil rights, or helping out poor people or people in war-torn countries, you'll find a whole lot less programmers stepping up to the plate on these issues, and for a totally sensible reason - it's not as relevant to them.
I'd like to propose an alternate thesis: Within any field, there will be a certain small number of people who have strong morals and are willing to disobey authority to champion what they think is right. At the current moment, there is a particularly high rate of activism within the "digital rights" field because the internet is comparatively young and people are still trying to figure out what rights you have.