RE: Postnatal exposure to household disinfectants, infant gut microbiota and subsequent risk of overweight in children

Epidemiology is not my expertise, so I am confused by the conclusion that household cleaning products “affected”, “altered” or “changed” fecal microbiota profiles given that only one fecal sample was collected from each child at 3-4 months of age.
“Associations with altered microbiota were most compelling for frequent use of household disinfectants, which showed reduced abundance of genus Haemophilus and of genus Clostridium.” Altered from what and reduced abundance compared to what?
Had a fecal sample been collected near birth and then at 3-4 months post-partum, I could understand the idea of changing microbiota profiles based on cleaning product exposure over the first 3-4 months of life. But I see no suggestion that this was how the study was conducted.
The study authors state as much under the heading of Limitations.
I acknowledge correlations between disinfectant exposure, specific microbial prevalences and overweight, but have no sense that the second is causally linked to the first without the pre-exposure microbiota profiles.
I thank you for your attention.