I'm sure it couldn't be that, where Alito is 'activist,' the constitution limits the government powers and Alito thinks we should enforce that. OTOH, where he is not, the constitution does not prescribe the expansion of judicial powers to made-up rights.
That's why discussing whether a justice is "conservative" or "liberal" should be irrelevant. That's the value of a consistent judicial interpretation. If you take two people, one a married, fundamentalist evangelical, meat-eating, gun-owning firebrand justice and the other a gay, devil-worshipping, vegetarian who believes in conflict resolution classes for naughty people, with an originalist judicial philosphy, chances are you're more often than not going to get the same decision.
That's not to say there can't be different interpretations even within the originalist philosophy. It also doesn't mean that personal views won't ever intrude....it does mean that it is less likely to happen if you are rooted in a particular discipline of interpretation. It also means you're less likely to drift and grow over time. I think the fact that Judge Alito has been on the 3rd Circuit Court of Appeals (one of the more liberal Courts) for 15 years and has shown no sign of leftward drift is one of the strongest arguments in his favor as well as a good demonstration of how a judicial philosophy grounds you.
One other quote from the article I found amusing was "In the Washington Post, Cass Sunstein examined Alito's dissents and found them "almost uniformly conservative." Cass Sunstein is so liberal, I'm sure he say the same thing about the Constitution itself!