The article can be confusing the way it is written. He starts off telling us that it is not the sun that is moving but the earth, revolving around the sun. Later he uses the term "sun is moving" several times.
Then, he says "For some odd reason, the winter solstice has come to be known as "the first day of winter" while the summer solstice continues to be called correctly "midsummer's day." I'm not sure what he want's here, does he want to call it midwinter's day? That would be odd.