Which interpretation was the author’s intention? Or was it meant to be ambiguous?
100% intended to be ambiguous.
Having seen the movie I can say that the characters are extremely rich, and are only “crazy” in the way that rich people can be eccentric, showy, and dramatic.
Rich Asians who are crazy.
Both at the same time.
This. It’s just a “clever” movie title.
Perhaps the filmmaker intended it to be ambiguous whether they intended it to be ambiguous. Is that less than 100% ambiguity or more than 100%?
It’s ambiguous turtles all the way down.
Strictly speaking, it’s a “clever” novel title. The movie’s named after the novel it’s based on.
Crazy people who are rich in asian heritage?
I believe at one point Awkwafina’s character refers to another family as “not just rich–crazy rich.”
Not in the book, only in the movie. Presumably to clarify that it’s not slamming Asians.
In interviews the author was careful to say that he meant “crazy rich,” not that he was demeaning the characters as crazy. But, you know that he knew that you knew the game he was playing.
The other two novels in the trilogy are titled China Rich Girlfriend and Rich People Problems, for what it’s worth. Seems more focused on the $$$$ than 
To me it reads: Extremely Rich Asians
Anything else feels like it’s flirting with bigotry. Which I don’t think the producers would want to do.
That may have been the intent, but the movie itself was pretty clear: they were not crazy, only crazily rich. Calling it a comedy (in the modern sense of the word) was false advertising. Not only did I not laugh, I could not bring myself to care at all about the characters. If I wanted wealth on display, I’d Google pictures of luxury settings.
The OP asked about the author, so I was replying about the book. The line was inserted into the movie to clarify that this wasn’t some racist jibe.