As has been noted a few times in this thread, if a player is booked for a foul for which a player needs treatment, that player doesn't have to leave the pitch after treatment. That is something the ref got right.
The ref cautioned the player who fouled Bruno, so Fernandes didn't have to leave the pitch. It's been the law all season.
If you want to argue the assessment/treatment on pitch wasn't 'quick' that's still not Mariner making the laws up, just being generous in his interpretation of a law that...
https://www.theifab.com/laws/latest/the-referee/#powers-and-duties
Injuries
allows play to continue until the ball is out of play if a player is only slightly injured
stops play if a player is seriously injured and ensures that the player is removed from the field of play. An injured player...