The message said they're from Chicago and there's a META LLC registered to him in Illinois since September 2013. Not sure what they do, but at minimum it seems like they've been using the name for some time.
If you're going to stake claim to such a common, short term as your corporate name, it's definitely obvious that you're risking legal conflict with other entities that may claim that name. There's no way they didn't know what they were getting into in trying to use that name (with or without Facebook wanting it).
But ever since a certain company decided to call itself "fruit", and then go on rampage attacking small players which themselves used to be called "fruit" under the petty reason that they are actually producing and selling "fruit", there is a sense in US that, as long as you got the balls and the lawyers, there is just no limit. Limits of the rules, even when written, are for "others".