Exactly as he should have. He was traveling for commercial purposes and cannot use a travel visa. Nearly every country in the world requires commercial travel visas if you plan to work in the country.
For a professional rider, these competitions are work.
Depends on whether you get paid even if you come in last place. If its only the top few that get money then I disagree. The article doesn't make it clear.
Sponsorships still pay you if you lose
The sponsored kayakers that I knew got free kit and that was about it. Admittedly biking is a bigger sport, so maybe thats the case there.