Playground Games mode cheat?

I started the seasonal PG event, got a very good team and all but one player on the enemy team simply quit after the first round. To everyone’s amazement from round 2 on, someone joined the enemy team (?!) in a car that’s not even allowed to take part in this event as it was an A762 vs maximum of D500 allowed.

This is how it was:

Next round the A class Traveller has joined and stayed until the end of the event:

This is the first time I see this since I’ve been playing Forza, which is more than a year ago. Can someone explain to me HOW is this possible, a hack/cheat? Or does the game try to rebalance the losing team by adding a bot?