It was the imposter. In the episode summer of loveSummer of Love Arturo showedis shown to have some knowledge about football, but in the episode the guardianThe Guardian Arturo showedis shown to have no understanding aboutof football and didn’t know what a team was Also.
Also, in the pilot, when Quinn got home from his first slide he went to Arturo to explain it and named the Einstein Rosen ponolski-Rosen-Podolski bridge, as if Arturo knew what it was but. But in the episode double crossDouble Cross, Arturo claimed that he had never talked to anyone about sliding. Does that awnser your question?