All you're doing is showing that the statement is ambiguous. If we read it to mean "there is a real person named spiderman who was bitten by a radioactive spider and now has superpowers because of that" then, no, that's not true. If you read it to mean, "there is a story in which there is a character..." then yes, that statement is true.But I thought we had already established that the statement was not true.
I don't see any problem with that. Yes, statements are ambiguous, but so what? That doesn't mean that a particular interpretation of the statement isn't either true or false.
No, some stories are true and some are false, but the fact that they are false isn't particularly important because we all know they are false.Stories are not true. But they aren't false either because there is no intention that they communicate the fact of any matter.
It really is false that a person was bit by a radioactive spider and subsequently developed superpowers. It's just not particularly interesting to point that out because we all already know it.