This point was already addressed in the research. It is tiring to see this low effort comments on every research thread, thinking that the researchers are idiots and there is no need to read the article to reject it.
Children's DNA inherited from their parents contains roughly 25 to 75 new mutations, which allows scientists to compare the parents and offspring, and then to classify the kind of mutation that occurred. When looking at mutations in thousands of children, IU researchers noticed a pattern: The kinds of mutations that children get depend on the ages of the mother and the father.
Later: Hahn, Wang and their co-authors built a model that uses de novo mutations—a genetic alteration that is present for the first time in one family member as a result of a variant or mutation in a germ cell of one of the parents or that arises in the fertilized egg during early embryogenesis—to separately estimate the male and female generation times[...]
So, it is saying it can measure results for male and female parents separately. But can their analysis of the "kinds" of mutations tell the difference between e.g. "30yo mother, 45yo father" or "20yo mother, 30yo father, plus lots of environmental factors that increase mutations"? The article doesn't make that clear to me.
The article links to the study (at "10.0.4.102" instead of a domain name?), but the link doesn't load... Ok, there is a working link at the bottom: https://www.science.org/doi/10.1126/sciadv.abm7047
I skimmed the study around all the matches for the strings "mutat" and "environ", and this was the best I found: Estimates of the error in our model fit do not show increasing error with either genetic or geographic distance from Iceland (figs. S6 and S7), the origin of the pedigreed mutation data used to train our model. Such a trend may have been expected if differences in mutational spectra were driven by genetic or environmental differences among populations.
The last sentence is actually ambiguous, but I think it's saying "If environmental factors tended to mess with mutational spectra, then we might expect to see X, which we did not see." It's still not clear to me how possible it is for there to be environmental factors that generate the same mutational patterns as higher age. And the only other "environ" match is in a sentence about what affects the age at which people have children.
An analogy for this one could be saying something like “I know it sucks when people say unkind things, but I think you’re stupid.” Acknowledging the problem does nothing to prevent it or resolve it. It just means at some level the person knows what they’re doing is wrong, and they aren’t self-disciplined or integrated enough to stop.
It burdens the (numerous) other parties with the effort, in the same way scientific results like this do.
The answer to GP's objection is not explained in the linked article, as far as I can tell.
The writers of a research paper have a vested interest in seeming smart and displaying their findings as a novel contribution to the greater corpus of research. It's better to think skeptically and critically about any new research paper than to accept it as fact.
Science Advances is open access, so no subscription is required. For those looking for the article: https://www.science.org/doi/10.1126/sciadv.abm7047