Indeed so.
But otherwise, this is a jargon issue. “Odds” is often used colloquially differently than the mathematical definition.
The folks at 538 really aren’t using the numbers the way a sports bettor would, either, but I can see how it may appear that way to the uninitiated - by which I mean, math dorks and degenerate gamblers (I exist in the intersection of the two, as I imagine several others do).
Oh, yeah? Wanna bet? 
When written in that form (3:1)? Can you show me an example?
Plenty of countries use decimal odds, and instead of showing money bet (stake) along with potential profit (winnings), they show money bet along with total returns (money bet plus profit, or “yield”), however; I know of no countries that use x:y format to express what you claim.
I don’t think they would call it “paying $12” in those countries. IME, it’s called “the return.”
Example for those confused. A 25% probability can be written as: 3:1, 3/1, or 300 (300 because for every $100 bet the potential profit is $300). For every $1 bet, your profit (winnings) will be $3.
The same can be written in decimal format as 4.00, which means a $1 bet will return $4 (your original $1 plus $3 in winnings).
That depends on the odds given by a betting site. 538 is a statistics site giving probabilities for a uncontested convention, they’re not giving odds and not accepting bets.