Allegedly it does appear that at least 12 people were injured in the Critical Mass. Luckily no one was killed.
One cyclist who was on the ride Camilo Colling, told the Brazilian website Terra Brasil that he spoke to the driver just before the incident, asking him to be patient and stop behaving aggressively towards the riders in his path and warning him that there were children and older people taking part in the ride ahead. The driver allegedly replied “Yes but I’m in a hurry” before ploughing his car in to the group of cyclists in front of him.
More details here.