If you were not informed of any other parameters, and you met the restrictions of the race, and you were in the exact same car as the other guy... Then I can't imagine.
Unless you bunted or bump-slid him... Maybe by accident? And he thought it was on purpose? That's the only "cheating" I can think of... that maybe you rear-ended him & caused him a penalty or damage or something??
I was in a pub shuffle race with some very fun friendly players. I was in a car that I had trouble w/ the braking, and I rear-ended the car in front of me approaching the hammerhead on the Top Gear Test Track... I bunted him into a penalty, but I didn't get a penalty. I could have gotten way ahead in the race because of that. BUt what I did was just waited & stayed behind the person I hit until their penalty was over, I didn't try to pass them until they were solid again, because I thought that would be impolite. After the race I apologized (I don't have a mic).
The person sent me a friend request after that.
I don't get bent out of shape about people bumping & scraping by accident, particularly in full races on tight tracks. Let's face it, it happens. But if I'm in the position where a blatant error on my part causes another driver an unfair penalty & I get away with it, I don't take advantage of that. When other people do, I wouldn't necessarily call it "cheating" as such... but it's also not right... or at least not fair.
But if there was no such incident in your case... I wouldn't worry.
If there was such an incident... most hosts will tell you after the race exactly what they thought was crappy behaviour. And most will boot you only if you do it again.
I've been in races where one person gets told off, but then they straighten up their act, and play continues and the peace is restored, and there's no further incidents.
Sometimes people are just sloppy, & need to be reminded to take some care. But sometimes people are deliberately disruptive, and I bet some hosts just find it easier to just assume it's deliberate & boot at the 1st sign of trouble.
But it could be the host was just a pride-sore joker.
Don't take it personally, whatever.
Just makes the point I mentioned on this thread:
https://www.gtplanet.net/forum/showthread.php?p=5347155#post5347155
There's tons of reasons some hosts give people the boot - that you might not think of!
Some hosts boot people who they think are not good enough, and some hosts boot people who they think are winning too much.
If they are the host, they get to decide. Even if it seems dumb & pointless to the rest of us. haha. You just don't take it personally, and move on.