I don't think it's a fuck off message at all. That would be just "fuck off". Why encourage recruiters if you didn't want to deal with them?

To me it says "don't just shotgun me with every rando candidate you have - I'll give you one chance, make it count". It's exactly the sort of thing you might say to a pushy recruiter you met at the bar who wants in to your business. To succeed, they must a) have a good candidate and b) understand your business (so they know that candidate is right for you).

And I'd say there's an enormous difference between what a software engineer does (spend months or years designing and implementing a system that is for a single "customer") to what a recruiter does (spend 1 hours of conversations/emails in qualifying a candidate who can be shopped out to any of a number of customers.).