Doesn't the article suggest the opposite. If populations are declining in untouched forests far from human activity, wouldn't that be evidence that human activity is not the cause of population decline
It only suggests that local effects are not responsible. That leaves as some of the possibilities: climate change, air pollution, other chemicals that still make it in to 'untouched' forests.
Microplastics have been found everywhere, from high mountains, to antarctica and deep ocean sediments. I am not claiming thats the vector responsible in this case but the human footprint is now everywhere.
The term anthropocene is not an exaggeration. We are changing everything on a planetary scale: light pollution, sound levels, chemical and gas abundances etc.
People think that if something is not immediately fatal its somehow ok. That the tragedy of our reptile brain wiring.
In reality all sorts of impacts will accumulate only imperceptibly slowly. We might be able to do something about some of them if they have clear cut causes and some easy remedy. Like the ozon hole. But its an uncertain arms race.