Yes after reading that and doing some of my own reading, my previous post was wrong. It looks like Facebook "crawls" the site to gather the metadata necessary to display OpenGraph properties (preview image, topic name etc) when a link is posted on Facebook, see:
https://developers.facebook.com/docs/sh ... rs/crawler
This is probably I have seen these hits coincide with my board being linked on Facebook and came to the conclusion I did.
I still think it's not in the same category as other bots. The only reason you want to add specific bots like this is control permissions and to manage sessions where the bot is opening lots of concurrent connections, like a search engine crawler. This Facebook user-agent doesn't do that. It just hits pages sporadically when a page is linked on Facebook. If you don't define it as a bot, it will be treated as a guest, and that is probably appropriate in the circumstances.