If someone is racially offended by it, then yes, it's racist.
While Green Mile is a movie that features a large black man with mystical powers and Tom Hanks with a urinary track infection, the term "Green Mile" could be referencing a number of things.
My understanding is "Green mile" refers to death row. Is the person calling Jawai a criminal? And is he being called a criminal because he is black? This could be seen as racist as in the US-where the term green mile orginates- The highest number of incarcerated people are "black" people.
My personal opinion is the world is overally too PC now, with all these social justice warriors and safe space fanatics, but that said - if someone finds something racist, then it's racist.
That said, if Hugh Greenwood ended up playing for the Wildcats, my friends and I (who are a bunch of mixed races) would have been calling him "Sunshine". After the star blonde californian quarterback in Remember the Titans. Would that have been racist?