I think a study like this is mostly worthless.
The issue here is that humans are a combination of their natural state (how they would be if they were raised with no contact, direct or indirect, with society) and social conditioning (the system of induced emotions and mental strategies that society instills in people to sustain and propagate itself).
"Committed relationships" are in the natural state most likely naturally living in a tribe, with probably little or no pair bonding/coupling in humans, while western social conditioning is about committed relationships, marriage, etc. with several very different flavors (traditional marriage, polyginous marriage, hierarchical polyamory, etc.)
"Casual sex" in the natural state probably "just happens", while social conditioning has a whole lot of mental ideas about with whom/when/how much you should do it, what it means if you do/don't do it, etc.
The problem with studying the natural state is that there are little or no humans living in it (and certainly none accessible to most/all researchers), and the closest animals, chimpanzees and bonobos, are significantly different between them in their sociosexuality.
The problem with studying social conditioning is that it massively varies between gender, location, subculture, age, historical period, and varies randomly between individuals.
So this study at best might manage to describe the average social conditioning that currently affects Mechanical Turk users (clearly chosen because it's easy and cheap to target them, rather than any attempt at producing quality research), and thus is pretty much useless.