This article is amazingly poorly written. Its content can be basically concluded as “Japan is called Japan because it is called Japan”, since it skips any methodical etymological investigation.

Check yorwba’s comment below instead.

I've always wondered why Japan come to be known with this name, and this article is a great explanation of it

It's actually a pretty terrible explanation.

They claim that English "Japan" came from Italian "Gaipan" due to "Gi" sounding like "J", apparently failing to realize that they misspelled "Giapan" twice, don't make the connection to the "Cipan" in Marco Polo's "Cipangu", imply that Italians traded with Japan despite Portuguese and later Dutch traders monopolizing most of the trade, and most importantly don't even mention the Middle Chinese pronunciation /ȵiɪt̚ puən/ of 日本, which gave rise to both "Nippon" and "Japan" due to different sound changes affecting ȵ differenty in Japan and China.

Wiktionary' etymological explanation is much better: https://en.wiktionary.org/wiki/Japan#Etymology

Thanks for the link, I didn't have the knowledge to see that the article was not complete