Firstly, the data were taken in 1999, in the midst of WWF's (now WWE) so-called "Attitude" era (think Stone Cold, the Rock, and D-Generation X) and near the beginning of ECW's end. In other words, wrestling programming was far more violent, sexist, and offensive (and, by some measures, better) than today. That is, it was directed at adults (twenty- and thirty-somethings), not teens.
Secondly, the correlations are actually weak (emphasis added):
There were significant correlations between frequency of watching wrestling on television during the previous 2 weeks and engaging in date fighting, fighting in general, and weapon carrying for both males and females, although the relationships were stronger among females than among males. The frequency of watching wrestling was highest among students reporting date fighting when either the victim or perpetrator had been drinking alcohol or using illegal drugs. When analyzed using logistic regression, the strongest relationships were observed between the frequency of watching wrestling and date-fight perpetration among females in cross-sectional and longitudinal analyses. These findings persisted after adjusting for multiple other factors.In other words, if one is under the influence of alcohol and/or drugs, and wrestling is on in the background, it's more likely that the behaviour in the wrestling program will be modelled by either oneself or whomever one is with. (Hey, drunk people can be annoying; I can relate.) I'm not sure why this is a surprising result.
Thirdly, the study itself clearly only cites a correlation, not a causal relationship:
CONCLUSIONS. For males and females, the frequency of watching wrestling was highest among students who fought with their dates when alcohol or other drugs were involved. The association between watching wrestling and date fighting was stronger among females than males. The relationship between watching wrestling on television and being the perpetrator of dating violence was also stronger among females and remained consistent over a 6- to 7-month time period.This has been yet another lesson in why reporters shouldn't try to report on science.