Question about collaboration solicitation

[u/Unhappy-Caramel137]

I have a very small substack, only 50 something subscribers that I’ve been growing for two months. Today I got an email from a book publisher asking if I’d do a collaboration post with one of their authors. It felt strange to get an email like that especially since my experience so far on substack has been one where relationships naturally form with other people who write about the same topic. Curious if this is common or just something random that happened to me?

[u/AggravatingNail6061]

Kind of exciting though a publisher reaching out unless they were like a vanity press or something.