Those type of traffic checkers are often largely weighted towards judging by domain authority, and are usally wrong for that reason, but in this case, seems they botted searches.
According to thehoth(semrush based keyword and rank checker, which in my experience has been very accurate for my own sites), wellhealthorganic only ranks in the top 10 for 4 keywords(and oddly, the "keywords" are their own entire URLs, not actual keywords), the highest vol is 720 a month. It appears the site gets approx 400-500 visitors a month. Outside of the top 5 keywords, it ranks 60-80 rank for everything else.
Even sites with 5,000 visitors a month have wayyyyy nicer looking stats on thehoth.
It certainly doesn't get 31m a month, nor 1m per month.
You can see the social share metrics for articles, most are 0, some are 1, some 3, the highest I see is 30. If this site had 31m visitors a month, the social share stats on the articles would be thousands.
Also, on all the checkers, it shows it's actual full URLs for it's top keywords, I've never seen that before. According to your screenshot, 6.8 million people google "wellhealthorganic.com" per month, as in search the url with .com in the google search bar rather than typing in the url in the url bar. Perhaps, they are botting millions of searches for their own url. They sell guest posts in the footer. It appears they've figured out a way to trick website traffic sites, by somehow inflating keywords(like it's own URL) into the millions, while not actually ranking for any real keywords. They can now just show the screenshot of their "31m" traffic to backlink buyers, and charge them a bunch of money for a guest post.
However they did it is very smart, but they don't actually get any google traffic.
Go ahead, and google "well health organic", surely, this 55 DA site which gets 6.8m visitors a month for the search term "wellhealthorganic.com" would rank #1 for the search term "well health organic", right? Nope, they don't rank for anything, including their own name, they get no traffic.
Simmilarweb and arefs traffic checkers are about as accurate as sites with social media influencer networths, and sites that say your 480 twitter follower account is worth $1,700.