Interestingly, it might not be the experiment but rather the experimenters themselves. When this study came out, I mentioned it to my girlfriend at the time (a veterinarian), and she pointed to research [1] that suggests a correlation between the presence of male researchers and stress in mice. It's plausible that if male researchers were present, the increased stress response could contribute to greater susceptibility to certain cancers (it was only the male mice in the 5G study that were affected).
I have no idea how the study was done or the genders of the researchers who participated, but it's worth considering that other variables may be at play. Perhaps it should be replicated under an all-female research environment if it wasn't originally.
[1] https://www.nature.com/news/male-researchers-stress-out-rode...