I'm not surprised.
When we are going backwards on women's rights, it will be reflected in the parts of the community most vulnerable to being shaped ie young people.
The more women are dehumanised, through porn, decrim of buying sex, TRA and MRA views of women as privileged and pampered, the less likely it is that young boys see hitting us as so bad.
I'd assume it reflects a desensitisation - these young men have seen violence normalised at home.
Not sure if it was this study or an earlier one, but Gen X men actually have better recognition of what VAWG involves, and it's unacceptability, suggesting that we are indeed going backwards in terms of education.