Not refuting your theory, but in all probability, you (like most others in the industry) have friends ("friends"?) that simply relay info to recruiters from these two companies. Poaching is often done that way.

Also, at least in my case, both Google and Facebook periodically reach out, years after our last formal interaction.

Had a recruiter working for one of my clients for a few years. They later left the company and joined the competition. Recruiter's past "success stories" all got contacted, not a week after.