Seafood is different, since the food chain can be significantly longer and more complex.
What is "minimal"? Bioaccumulation isn't a magic meter that says "everyting below this trophic level is safe to eat." It depends on the persistent toxin ( I choose the word toxin because bioaccumulation can occur for chemicals beyond heavy metals, like organochlorine pesticides ) that you're looking at, and what is the safe dose for humans.
E.g. let's say you have pesticide A and pesticide B. Cattle eat a certain amount of feed per day. At time of slaughter, pesticide A and B have a certain amount of concentration in fat tissue. It doesn't matter which has the highest concentration, it matters which is less safe to humans and at what concentration it harms us when it accumulates in our own tissues.
Chickens naturally peck about for worms, insects, seeds, etc...
https://nutritionfacts.org/video/cannibalistic-feed-biomagni...
IIRC, such things tend to accumulate most in the fat, fwiw.
Plants definitely do have different rate of heavy metal accumulation, and presumably other toxins, though I'm not aware of any evidence that a typical feedlot diet of corn+soy is better than all grass with regards to potential toxin bio-accumulation. This isn't to say that there may not be other health benefits to raising pasture animals on 100% grass.
Animal-based animal feed is certainly a thing, though in my experience "100% vegetarian" diet is often the the cheapest type of meat. Organic meat, while more expensive, guarantees it will be raised "without antibiotics, added growth hormones, mammalian or avian byproducts" [0]. This does seem to exclude fish-meal type feed, which presumably is allowed to be used in organic meat production - though I'd assume its more economical to use a plant based feed in almost all cases.
[0] https://www.ams.usda.gov/sites/default/files/media/Organic%2...
Grass fed beef is more nutritious than grain fed (easily googled).
Grass fed beef is leaner and has a noticeably different fat composition (easily googled). This is pertinent to bioaccumulation because fat is usually where stores of toxic chemicals are at their worst, iirc.
Grain fed beef is typically fattened up in feed lots which can be vectors for disease (easily googled).
Grass fed is typically exposed to fewer pesticides. Sources:
https://nutritiouslife.com/eat-empowered/grass-fed-beef-orga...
http://www.certifiedgrassfedmeats.com
I'm not a stickler for only eating grass fed beef. However, I have gone through periods where I was extremely ill and found that it was very worthwhile to only get meat labeled "grass fed." I was much more able to tolerate it and it didn't severely acidify my system the way meat sometimes can, which is consistent with the fact that grass fed beef is much higher in Omega 3 fats.
I'm not trying to lecture anyone, dictate how they should eat, etc. I was just making the observation that if the point of the article is to persuade, then they missed a potentially big detail in terms of arguing from a position of enlightened self interest rather than morality. It's a detail that's often overlooked by people trying to persuade others to "do the right thing, eat less meat!" and another reply to me cast a bit of light on possibly why it is so often overlooked.
I have a sheep farm. We have to be very careful not to confuse the sheep grain ration with the chicken feed. They look exactly the same, but chicken pellet has copper in it, and sheep can't metabolize copper. We also have to be careful not to accidentally buy or feed goat ration for the same reason.
That said, "grass fed" is complicated too. In a lot of places the cattle are grazing on unimproved rangeland. It isn't even fertilized. But in some places the farmers will explicitly plant forage crops such as wheatgrass; these will typically be fertilized, and possibly treated with herbicide or pesticide. Fertilizer is usually an industrial nitrogen fertilizer, but it can also be composted manure. I know of at least some farms near where I grew up that were at points treated with concentrated sludge from sewage treatment plants, in which case you would definitely expect to get heavy metal accumulation, even in straight grass fed animals. Happily my family never went that route.