The flaw in your reasoning is: why hasn't he yet?
He either hasn't been trying in which case there's a chance that he hadn't tried with spider-man and thus wouldn't know.
Or he has tried and failed which means that he might have tried and failed with Spiderman as well. It's not like spiderman goes around telling everyone all about himself. There are certain things that a person might not easily be able to figure out about spider-man.