Diego Rivera ufo sighting?

Just was reading Diego Rivera's autobiography, you know the mural painter from Mexico right?

So i was reading the book and found a paragraph where the author describes seeing three spheres on the sky, it is not really a very detailed description but once you have read the text you will find that it resembles a lot of what we today know as UFOs, or maybe not?

The book, turn to page 94:

books.google.com...

Maybe those were just some asteroids or something like that, but who knows?

By the way, this was on 1928 or something like that, long before UFOs were "discovered" by the media or people in general.

What do you think?, not that much information I'm afraid but interesting anyway.