Facebook leaked your IP people you communicated with, not that IPs are that sensitive in the first place. It wasn't a big deal.
I still have these mails in my inbox. People who I've never met nor conversed with online in my life.
And whether it's sensitive depends on the context. Revealing one's IP reveals their location, and I can think of many cases in which this is sensitive information.
Unless someone knows exactly how the internet works, getting their IP address via social engineering is trivial. Facebook's behavior was not a big deal, though fixing it was a positive thing.