When did Jamaican become a race?
The comments of this 'fan' literally cannot be racist, as nothing said was about race.
Now, maybe you could say the comments were culturally insensitive, as I suppose implying that all Jamaicans are nothing more than bobsledders seems like it fits the description of stereotyping, but that is about the extent of the derogatory nature possible here.
As for mistaking his identity as Jamaican, when Mills is in fact a Pacific Islander, I'm not sure that qualifies as any type of derogatory remark. Not unless its being used in a way to imply Jamaicans are somehow inferior, which I don't think that was what happened here. It's probably rather ignorant, however.