Ah interesting, good catch! Although even though it was signed by royals of Aragon, Castile, and Asturias, it states that it "divided the newly discovered lands outside Europe between the Portuguese Empire and the Spanish Empire (Crown of Castile)". So how does that work?
Discussion
Who does? Wikipedia -- not the Treaty or anyone who was there when it was signed.
It's an anachronistic expression, and it's specially ridiculous to invoke it at that specific time. Neither Ferdinand nor Isabel ever claimed the title of Emperor/ess.
You can forgive it in a non-academic and often extremely biased and manipulated source like Wiki, but not in a more serious text or if you want to be accurate.