Did you read the abstract? The parasites are in the gay and straight community, but since they appear to live in the anus they are more commonly spread by anal sex which is common in the gay community. This is essentially the same as saying HIV makes people gay because it is more prevalent in the gay community. But obviously that is a correlation with a clear causation- unprotected anal sex with multiple= higher rate of spread of HIV, homosexual community has a higher rate of unprotected anal sex with multiple partners.