Facebook User Numbers? CRAZY Any explanation?

I was messing around on Facebook today and found something pretty interesting.

If you type the following into a comment box: @ symbol followed by [number:], Facebook automatically replaces the symbols with names.

For example: if you enter @[4:] into a comment box, it will automatically change the comment to read 'Mark Zuckerberg.' Entering @[5:] will render the text 'Chris Hughes' and entering @[6:] will render the text 'Dustin Moskovitz.'

Any explanation for this? Theories? I can't imagine this is intentional on Facebook's part. Pretty interesting, IMO!