I'm going to qualify what I'm saying by stating that this is a guess. Without further interviewing or reviewing the profiles of the population of the study, I don't think anyone could seriously speak more strongly.
Capitalism is founded on the rules applying equally to all. If Alice creates a widget that outperform's Bob's, she's going to earn more money. Both were free to produce whatever they wanted according to the same rule of law, but one performed better than the other. It's natural that willing participants in such a system observe that for the system to work, law must be followed to create the closest state reasonably possible to an operational environment equal to all who participate.
The mentality of socialism places an emphasis in closing the gab between the inequalities of outcome. Here, Alice may produce a widget that outperforms Bob's, but others will frown upon a wide income gap between the two, regardless of how much better Alice's widget is. There are negative impacts perceived in such a wide income gap. In these circumstances, one who subscribes to the ideas that underpin socialism would tolerate working outside the protocol of the rules of producing widgets for the sake of preventing Alice from outperforming Bob to some extent. And if one happens to be Bob, breaking the rules of the game of economics is actually contributing to the greater rule of keeping the income gap from becoming what such a person considers too wide. It may strike Bob in his view of what's fair to break the rules.
As for some final thoughts, I don't think anyone can reasonably conclude that people who advocate capitalism are people who respect rules and those who advocate socialist ideas are not. Rather I think that the operational environment entices people to behave in certain ways. Put a raving capitalist in a socialist system, and he may not behave according to the rules. Additionally, in a system, such as socialism where execution of the rules and control of resources resided more so in a centralized authority, the most pertinent rule is learning to gain favorability with that centralized authority. All other rules are subordinate to that.
Just for the sake of full disclosure in case you've read this far and are still wondering, I mostly prefer a capitalist economic model over a socialist one.
Cheers, and happy Slashdotting.