There's no way of knowing which gender is truly more aggressive than the other when it comes to relationships (lesbian, gay, transsexual, straight, or bisexual) and its impossible to be 100% sure when it comes to the studies that record data from others, because people are not always honest when comes down to it. This is a very tender subject and people are not always eager to discuss matters of partner abuse or to report it to authorities.

While it the study may be very accurate, it has also been shown that woman tend to be more open about more tender subjects than most men, because most men don't like to admit they've been beaten up by their partner (male or female) and taking this into consideration, its nearly impossible to be certain that everyone is telling the truth (unless of course we add security cameras all around them or have someone follow them 24/7, but that wouldn't work for obvious reasons)

So while this study may be accurate its almost impossible to tell whether its true or not, and if its true and homosexual women tend to be more violent than homosexual men, than there is some reasons why this could be (verbal disagreements that turn physical, mood swings, pms etc)