It was a case of "if you work here, you're certified as knowing your shit" and "it's not what you know, it's who you know."
As said, I was self taught programmer, so for me this was a type of validation which meant the job had more significance for me at the time. If I could make it onto the Facebook staff, I was legit. It took me a lot of hard work and dedication to overcome that mental set back. I think all of us self taught devs have a lingering suspicion we're not good enough, not vetted enough, not seasoned enough, etc. Having a major life goal (@ 22yo) sitting at your doorstep and missing it due to your own shortcomings pretty much brought those back of mind doubts to the forefront and crushed my self worth, for me.
Luckily I'm not a "ah well, guess I'll go cry" kind of guy and adhere more to the "oh yeah?! well fuck you too!" attitude and having this happen to mean early in my career did nothing short of light a fire under my ass to be better than I was and better than I think I need to be. The salary offered for the position was about $28k more than I was making at the time and through a lot of self teaching, negotiations, and job jockeying I was making more than that position offered by about $5k within 1 year.
Despite all of this, that FB denial still has a tinge of "you suck, give up, go home, raise rabbits or something... you'd be a good ditch digger..." that still sits in the back of my mind reminding me constantly that some goals just aren't achievable... even if I don't want them at this point in my life anyways.
/rant
Then, a few months later I got another recruiting call from them. Then another. It didn't stop until I suggested they create some sort of engine for searching potential candidates to make sure they weren't wasting anyone's time tba the calls stopped. Once again, they didn't seem to like my idea ;p
I think this persistent inquiry from the large companies is an attempt to gauge the market and basically waste peoples' time. They interview in the hopes that the person will fit enough to slot into an available headcount, but it's pretty generic and highly unspecific. It's something like, hey, if you're looking to change jobs, come spend a day and take a chance that we'll be able to find something for you. I think it biases toward cookie-cutter employees and is by no means an indication of real interest.
It was in Switzerland though, and I'm not, my ethical qualms about working for Google aside (and I know I wouldn't be hired as I could never bring myself to lie about their privacy invasion, Google Glass being a stupid idea, Google+ being hideously invasive and useless, etc.).
Personally, the weeks following my interviews with one of those big players saw me approached by a couple of established start-ups and a major financial company - far more attention than I'd ever received previously.
The word you're looking for is "company".