Just finished a race where I had guys at 3rd and 5th, and got a splashscreen saying something in the lines of "objective met, here's $1M", but when I look at my finances screen it shows $1,620,000 for prize money and $580k for sponsors, which is equal to the amount I get from my money-sponsor anyways.
Here's a screenshot of my finances just after the race today:
https://s18.postimg.org/tmb49h2w7/finances.png
And here's the sponsors:
https://s3.postimg.org/umm2pnmdv/sponsors.png
It also said the "Here's 1 million" again after this race, and my prize money exactly the same as after last race even though this time I managed to 1st and 3rd.
Your prize money comes from meeting your objectives, which is both of your sponsors rewarding you a combined total ($1.1m + $540k) of $1.62 million.
I think what is happening here is the race viewer isn't showing how much exactly you were rewarded and is simply showing $1m, instead of $1.62 million or $1,620,000.
That could definitely be a cause to your confusion as well as lending confusion to other players who are thinking the same or similar thing you are.
If the Finances page receives an update that creates a list more detailed I think the various levels of confusion with the Finances page can be resolved.