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.
Plus, Ruby is big in the CM/operations/deployment world given the popularity of both Puppet and Chef.