I see those as different skills sets and usually different teams but I don't think there are strict lines in between them. Product Marketers should own the story, the core positioning and messaging, the surrounding context / thought leadership and GTM strategy. Ideally there are counterparts in integrated marketing, campaigns or growth marketing to help make that come to life.
But I think there's also what is ideal on paper and what is practical in real life. More often then not those integrated brand / campaign teams are swamped and not only serving the needs of product marketing. As a result, PMMs will more often then not need to stretch into what it specific assets and content needs to be created - whether that's videos, ebooks, blog posts, etc. And quite frankly, your partners in marketing will thank you if you come to them with ideas and they you can brainstorm the best path forward.
When I am hiring PMMs the core positioning and messaging skills matter the most, but I also want to know that they can stretch to think and how should this be brough to market.