It was racist in the same way that any criticism of Obama here is immediately called racist by some idiots in the media. If a liberal had tweeted the same thing, they would have called it a celebration of diversity. This athlete had supported a political party that the Olympic big shots had no time for. Thus, they lept at the chance to make an example of her. Calling the party extreme right wing nazi, etc, is also meaningless, since we regularly see mainstream republicans called the same thing here. The fact is the party is legal and has substantial support in Greece.
Did you check out their policy positions: http://en.wikipedia.org/wiki/Golden_Dawn_(Greece) And how about their dainty little emblem? http://en.wikipedia.org/wiki/File:Meandros_flag.svg Doesn't ring any bells?
When you work backwards from an opinion (pretending to be a conclusion), for example, "Obama is always bad", or "liberals are always bad", you will sometimes find yourself in bizarre alleys, like supporting Golden Dawn.
I don't really know nor care. Clearly the "mainsteam", ie far left, parties in Greece have produced a disaster. I do find it interesting that some other posters here who know less than I do probably about it can confidently describe it as extremist right wing nazism.