I think you misinterpret the words. Equivocal means that it's unclear from the study if there's a causal association while negative means no association was fou

I think you misinterpret the words. Equivocal means that it's unclear from the study if there's a causal association while negative means no association was found, not that EMF reduced incidence of gliomas. Also, an important quote in the description following that table: "The association of glioma and acoustic neuroma is stronger among long-term heavy users of mobile phones, which is also the most extensively investigated exposure source, and in some cases the onset of tumours was related to the side on which the device was handled."