First of all their games are provably fair so you can verify your bets easily, if you think there is something wrong with the bets then prove it.
Hundred of red bets in a row sounds bad but it is something possible especially if you set the game with the highest risk (red) although the chance is quite low.
I believe this guy is new to gambling or just an immature kid who started gambling a few weeks ago. I don't want to blame him for that. Sometimes, I get angry with the casinos, thinking they were rigged. Otherwise, I wouldn't lose whenever I place a max bet on them. But the reality is something else. I did not have enough patience to gamble steadily. Instead, I was rushing and losing.
We saw a lot of rage and angry players on chat rooms who quickly got muted for their behaviours. These types of people exist, and I believe they will learn over time and stop complaining after some time.