Yes, I also used Chef. But I don't think that is enough reason to market a language as beeing a "FB" one. Because in that way you can market that 80% of the companies use ruby.
Probably not their public facing website, but most companies run tons of code you'll never see. I've done ColdFusion since 1999, and while it's not a language the cool kids use, I've come across tons of large companies that use it for internal HR sites, internal content management, etc.
That guy isn't a Ruby developer -at- Facebook; he writes Facebook Platform apps in Ruby. With that being said I'm sure there's something in Ruby somewhere at Facebook - in an organization that size, there's room for a lot of best tools for the job.
Plus, Ruby is big in the CM/operations/deployment world given the popularity of both Puppet and Chef.