They cite some issues with the study. One of them is that the confidence intervals don't seem to add up and the incidence numbers don't look like the general populace for the control group.
I skimmed the article (it's quite long) found the criticisms weak.
> No data published; for Szmigielski (1996) it is implied that there were two to three brain tumors in the exposed group, in which case we imply that the 95% CI for brain tumor is incorrect.
> Several of these studies did not follow workers after they left the job of interest (Garland et al. 1990; Grayson 1996; Szmigielski 1996), with the potential for bias if individuals left employment because of health problems that later turned out to be due to cancer; this might especially be a problem for some types of brain tumor, which can be present for long periods before diagnosis.
The above two criticisms are only regarding the brain tumor incidence data, which is not the most significant finding in the paper.
> “Expected” rates in Szmigielski (1996) paper appear to be incorrect, according to the Royal Society of Canada (1999).
Link is broken, and why Canadian cancer incidence rates are assumed to be equal to Polish ones is not explained.
> Significant excesses were reported for several cancer sites not seen in other studies, and for cancer overall, suggesting possible bias.
Not sure why reporting what you found suggests that you're biased, but okay.
