Mauritania did not become a province until 44 AD (and even then, provincials were non-citizens by default). So here we have a barbarian who became a gladiator, one of the most socially reviled professions together together with all kind of entertainers, but who is also somehow a Roman citizen. Well done. Cannot wait to see what kind of fantascientific social path he followed to do that. And I presume he's the player's retinue, which is another gem, since an aristocrat associating with a gladiator or a former one was a big, big, big no-no. So you can be a patrician woman who is a military leader (an abomination) who chums it with a barbarian former gladiator (another abomination).
This is not that simple. Good, popular gladiators had a celebrity status. Many free people, not always only those who were poor, were becoming gladiators out of their own will. There were cases of patrician daughters falling in love with gladiators and then running away together. Gladiators could become rich and famous, even if their formal position in society was low. Few patricians had used gladiators as bodyguards.
Famous, retired gladiator getting a citizenship status seems very unlikely, I agree. The question would be if a popular retired gladiator would even want to be citizen because he already had all he wanted.