At first I also thought it was a clear swallow. In slow motion, I think you can clearly see from the defender’s foot that he hit something when he lowered his right foot. After repeating the scene 2-3 more times, I was able to see the contact relatively clearly. The Mainz striker hits the player on the inside of the thigh/knee when lowering the right leg. Even if the contact wasn’t strong and the attacker falls very theatrically, it’s a clear foul for me.
In the previous handball I would have clearly decided it was a criminal offence. But I think that people are a bit biased here, since in comparable scenes in the Bundesliga the decision is almost always based on handball. From a purely technical point of view, it is justifiable to let it run its course here too. So it may well be that similar scenes are not whistled in Romania.
Overall, I would probably be pretty well served if a scene like that was whistled against my team. From a neutral perspective, however, I would argue that at least it is not an absolute wrong decision. In principle, I don’t believe in rehabilitating referees who were involved in match-fixing. But I don’t know the referee or the whole topic and would say, at least in the scene, that it has nothing to do with it.