...Aside from prize cars, there aren't really any hidden things in a racing game that would be considered 'spoilers'.
This isn't Harry Potter, it's GT..
I've never read or seen a harry potter so that remark has more to do with yourself.
But I've played a great ammount of racing games and there are allways many things that can be spoiled. Just that you want to know everything now allready doesnt mean other people want to know everything before they played it themselves after waiting 6 years.
That's why I think that people like rdm shouldnt be praised, they probably have a stolen copy of the game, let people know it on the internet to feel important and spoil everything they think is cool. This may not be true for rdm, maybe he is Kaz his son and got the game from him early but that clearly isnt the case for most people who are playing it allready.
To complete my answer I'll give you some examples of spoilers in racing games:
Things that you can unlock such as modifications, paint, tracks, special events.
Suppose you get a cooler garage at some point, I wouldnt want to see pictures of that.
The cars you race against in every event.
A bunny or deer crossing the track. I would find that funnier if I hadnt heard it allready.
A sign saying something fun.
Driving lessons by Clarckson, Hammond and May in the coffee cup (That would be cool but I dont want to know it now!!)
The Top gear special episodes in full hd in turn for credits or every time u smash a really hideous car with a piano.
Some sort of trick about how to win an endurance race easier (way too early for that and should be labeled as a cheat)
And I could think of many more
