Reading through the article you shared just now, I can’t say it’s causing any issues or not with my birds really but I wonder if certain pine species are worse than others, they don’t exactly tell you what species was used.
I assume shavings are byproducts from the mills, tractor supply “where I get mine” doesn’t exactly say however and most likely it’s sourced from numerous species. It’s off subject but I wonder if some species wood is better/worse in toxicity. I know ponderosa and Monterey pine needles are more toxic than some other species, maybe the wood is also.