expressions - ''some theory'' vs ''some theories''

I was wondering which one of the two is correct:

• ''he had some interesting theory to share''

or

• ''he had some interesting theories to share''

The latter sounds correct, a friend backed me on that one too, but I'm curious to know why. In this context I'm referring to someone who was putting forth a theory on human nature - as I read it in an article. Technically speaking he only has one theory on HN, not 2 or whatever. Therefore I would like to understand why theory, when put like this, has to be plural because it is kind of misleading I think. Is it just idiomatic?

Thanks a million!