You are misrepresenting the result. They found that IPV was higher (not “much” higher) in interracial couples, but in interracial couples the IPV most more likely to be mutual, i.e. both genders are victimized, than in same race couples. It should also be noted that gender/race breakdown is not reported.
What they said was "interracial couples demonstrated a higher level of mutual IPV than monoracial white couples but a level similar to monoracial black couples".
In other words, inter-racial couples see a violence level similar to black couples. And black domestic violence level is high. While it's hard to get the federal data, in Oklahoma, for example, blacks committed 23% of domestic homicides while being 7.4% of the state's population