From the article: "So far, Java seems like a stinker to me. I've never written a Java program, never more than glanced over reference books about it, but I have a hunch that it won't be a very successful language."
I think that pretty clearly says that (at that time) he didn't think it'd be very popular.
So, you think popularity is success? I think that when Paul says "success", he means "winning" in an old sense that "those who adopt X have a better chance at winning" whatever it is. Just because the language is widely used doesn't mean it's contributing to the success of the adopters.
So how would you propose measuring "contributing to the success of the adopters" ? It seems that there is no way to either prove or disprove the statement hence any statement about the "success" of a language could be claimed as valid/true.
I think that pretty clearly says that (at that time) he didn't think it'd be very popular.