Curious what exactly includes the "seen" feature? If I have 30 tabs opened in my browser, facebook being one of them, does that mean every message would be marked as "seen" even though I haven't visited that tab for hours? How does it work on mobile? Do push notifications also count in the "seen" since I can see and read the message on the lock screen itself.
This is the only way the number could've slipped into Facebook servers. Still, sending fake friend request SMSes to the user when they don't even have an fb account is totally unethical.
Guess your comment is actually half-thought. I'm the person this blog post is talking about. And I'm pretty sure, I (and none of us in my family) even remotely know this 'advancetehri' guy. And who the hell has a name like that?
Also, when I clicked that link and when @iambibhas clicked that link, we both got immediate friend request from 'advancetehri'. (We blurred the link because it exposes the full phone number to anyone who clicks it) Rings a bell?