To be fair, “estar” in Spanish means “to be (something-ing, something-ed, someplace, or in a temporary state)”. That said, estas (Esperanto) and estás (Spanish) are not homophones because their stress patterns are different.
Also, I don’t think Spanish has a one-word translation for “esperanto”. “Esperanza” means “hope” in Spanish, not “one who hopes”. I think “esperador” means “one who waits”, “esperanzado” means “hopeful”, and “esperanzador” means “encouraging”.
As for me, I know enough Spanish that Esperanto doesn’t sound like Spanish to me (though I’m not a native speaker). The sounds of Esperanto and Spanish are kind of similar, but not identical. For example, the voiced stops in Spanish are fricatives a lot of the time, and /j/ can become a fricative in Spanish but not Esperanto. Also, the stress in Esperanto is completely regular and the stress in Spanish isn’t.
I’m actually kind of curious how much Spanish geneva_convenience knows. Maybe I’ve actually underestimated them, just because they made some spelling errors.
I think it’s because Esperanto uses many word roots which have a similar shape among various descendants of Latin, so people who speak those languages have an easier time intuitively understanding those words. I think this occurs for some Germanic and Slavic languages as well.