The "study" that you cite is well founded by science. Numerous experiments in game theory bear it out.
However, it doesn't explain capitalism versus socialism. Instead, it examines how people behave when they perceive others have a free ride. Folks who think others are getting a free ride tend to work less and put in less effort.
Is socialism a free ride? Capitalists will say it is, that people are getting something for nothing.
However, the exact same complaint can be placed upon the door of capitalism. Nations without taxation strategies that favor the redistribution of wealth (broadly: capitalist nations) tend to have wealth accumulate, to some degree, in families. Decedents of those who did work hard to earn their wealth are born with silver spoons in their mouth. To other members of society, it is those children of the wealthy who got the free ride.
In short, while the anecdote is scientifically accurate, it does not describe the difference between capitalism and socialism as much as it describes a much more basic form of interaction between people.
Or, to put it another way, there are free rides that diminish individual interest in excellency in both capitalism and socialism.