I haven't read the Wikipedia article, but the quoted claim that Columbus thought the Bahamas were Japan is just nonsense. In those times Japan was a completely unknown place and it was not until over 200 years later that Japan began to be differentiated from China, which was known as "Cathay" (after Marco Polo).
In his report to Isabella after his return in 1492, Columbus announced his destination as "the Islands of India beyond the Ganges". Elsewhere in the same report he refers to land masses as being part of "Cathay", but this is just a generality because India was considered to be part of the continent of Cathay (China), which it actually is.
Columbus did not have an accurate idea of the distances involved, so he did not realize the presence of the Pacific Ocean. For him, the islands he encountered had to be part of India because they had no notion of any other place besides.
Even long after Columbus mariners did not understand the vast size of the Pacific Ocean, which originally they called the "South Sea", and thought it was much smaller and lay to the south of the Americas. It was not until map makers like Amerigo Vespucci and others began to carefully plot things out, that it was realized they were dealing with an entirely new continent.