History is more than a collection of names and dates, but at least as to names and dates, it tends to be accurate, right? Well, maybe not.
When Winthrop arrived in the colony, another man, John Endecott, had already been appointed as Governor. But Endicott was not the sole Governor. Instead, he was the "Governor in the Colony," while another many, Matthew Craddock was the "Governor in the Company" in London. Due to a political crisis in England which caused King Charles I to dissolve Parliament, Craddock proposed that the split governorship be transferred to the Colony under a single office. Craddock did not want to emigrate, and Winthrop was chosen from among three candidates.
Thus, Winthrop was the "first" Governor who did not share the office. Both Winthrop and Endecott served many additional terms as Governor.