According to the LessWrong survey 61% of the 18 Moldbuggian's prefer monogamous relationships while only 53% of all LessWrong people prefer them. I didn't calculate whether the difference is statistically signifcant

It isn't, at all. Back of envelope calculation:

Standard deviation of binomial distribution not too far from 50-50 is sqrt(N)/2 = sqrt(18)/2 or about 2 out of 18 = 11%. The Moldbuggians are 8% different from all of LW answering the poll, clearly an insignificant difference.