I couldn’t find that blog but I traced your quote back to a Pakistani article. While I can’t vouch for the inks used in Pakistan, the inks used in the USA are safe to compost.
The blog is from Cityfood Growers and they are from Austalia. As far as ink being safe in the US. The federal government namely the EPA considers it toxic and requires and issues permits for it’s disposal. The newspapers are losing money and will buy it from the cheapest supplier. Who maybe getting it from China or Pakistan where there are less safety regulations. Do you require a hechsher for vegetable oil or do you just rely on the manufacturer?