Bullshit.

From actually looking at the article:

King's chief of staff, Sarah Stevens, told The Washington Post that King thought the woman was referring to the "leftist media" when she mentioned dirt — not immigrants.

"We quoted Representative King at length, on purpose, to provide readers with all of the context for his remarks," reads an editor's note on the article. "Steve King never mentions the media in his remarks.

And looking the "quoting at length":

An audience member asked, “Hey, how’d you do pheasant hunting?”

Rep. King replied: “I better not say so, because ... if I told them then the animal rights activist will go ballistic. And so I tell them, this is my answer, I’ll say ‘it was a beautiful clear, still day, an October day in Iowa, the sky was blue, the air was moving just a little bit, and the sky was so full of feathers that one could be convinced the angels were having pillow fights.’ And we were well fed, I made a big ol’ batch of my patented pheasant noodle soup for everybody. It took us two days to eat it all, but everybody loved it. When I get it all put together then I put about a half a dozen jalapeno peppers, just whole, drop them floating around in there. It scares off some of the people so there’s a little more for the rest of us to eat. I raised a bunch this year, and they don’t have enough bite. I guess I’m going to have to go and get some dirt from Mexico to grow the next batch.”

[Laughs]

Audience member: Trust me, it’s already on its way.

Steve King: Well, yeah, there’s plenty of dirt, it’s coming from the West Coast, too. And a lot of other places, besides. This is the most dirt we’ve ever seen.

What began as a story about his pheasant hunting trip, turned into, what seems, a veiled jab at Mexicans—as understood and promoted by his audience—innuendo about Mexicans or Mexican Americans as “dirt.” Iowa does have a topsoil depletion problem, but it’s hard to imagine that the audience and King were discussing the shipment of soil from out of country or from California. More likely, King was indulging in dehumanizing rhetoric about immigrants who come through California from Mexico, or from Mexico, directly.

So the article straight up admits that it's just speculating. That's hardly "verified."