In any event, if you are saying 500k USD, that most certainly isn't retirement money, and it puts your comment back into perspective. Small potatoes population and small potatoes money.
Income - Expenses = Savings
Savings + Growth Rate + Post Tax Rate = Your fund of money accumulated for retirement
If we where to put in the 500k USD at the end of every year in to a investment bank account and multiplie it with x (for the number of years) , with 5 precent intrest and include the capital return like we do in a simple geometric series in basic math/finance, it could be retirement money long term if placed/invested well (that is me assuming he and his team are not sophisticated investors) and also planning to retire in a place where it is fairly cheap to live, not in Manhattan, New york City, more like a small town in Sweden. Dude comes from humble beginnings and sometimes has the tendency keep living like that, like when he stays in a old used boat when he is training in San Diego, California. Or travel with the city Subway in the capital of Sweden, which finally had to stop because it took up too much time for him getting stopped by fans wanting to take selfies with him every minute and so on. He is very far from some "paycheck to paycheck dude", buying more liabilities as his earned income goes up.
Because other than all of the sponsors he also has his own company where he has an income from selling apparel (like T-shirts), gear and stuff like that mostly through a webshop (you kind find them in other stores too), apparently he makes plenty of money from that too, basically an asset that produce cash flow., the brand is big in Sweden (It is far from unique with him, both you and me know that several other fighters has done the same for decades).
He is also a investor of his money, among other in restaurants.
And when it comes to population in a country we also have to look at stuff like purchasing power, in sweden it is strong, Sweden is not Haiti, it is a pretty rich country with an average net salary $40,000 (annual).