Facebook has a vast array of technologies in use, from the top to the bottom of the stack and across a wide breadth of problem domains. A lot of the time there are competing technologies.
No one engineer at Facebook is familiar with the sum of technologies worked on by engineers at Facebook.
It stands to reason that recruiters are in the same boat.
So if someone comes to you and says "I've used Oberon, which is like Modula", do you know if they're correct? You don't, really. They very well may be. But the recruiter may also be dealing with one of the three dozen hopefuls every day who are desperate to pitch that X is similar enough to Y that they should be given a chance.
The recruiter was in the wrong. But at that size, there will always be recruiters who are in the wrong. It's luck of the draw. I've dealt with two Facebook recruiters in the past 4 years: one who misunderstood my résumé, another who understands it quite well. These days I don't take it personally.