Beef cows are accumulators. And their feed often contains plastics.
And you're right, there's also: plastic from water sources, plastic in the field that gets taken up by the gras, supplements given to the cow, plastic in the cutting board the meat was cut in, plastic the meat was wrapped in . . . it's hard to get plastic out of your supply chain.
https://www.primalmeats.co.uk/wp-content/uploads/2016/12/gra...
But nobody said it was coming straight off the ground!
https://thumbs.dreamstime.com/b/cows-eating-trough-made-blue...
https://c8.alamy.com/comp/2CFFY4J/hay-bales-wrapped-in-heavy...