The spammer in question had previously posted a bigger result, but the writeup was so badly written that some people in the field wrote a new, readable paper with the same result. In their abstract, they specifically cited him and said that the proof was so unreadable that they were unable to follow the details, and they had no choice but to write their own proof. (The spammer's proof also used math that was advanced enough to be far beyond his knowledge.)
My pet theory is that after this embarrassment, the spammer saw that nobody was able to verify his argument. Now the real problem is that his paper was written so badly that nobody could understand it (in math, you can't verify what you can't understand), but somehow he thought that the problem was that he didn't add an experiments section!