Facebook bug?

As a result of a discussion elsewhere, I googled someone and discovered a facebook page of someone with that name - wasn't them unless its a very old picture! Logged out of facebook - from my home page (on that site). When I next login the first page it shows me is this:

as you see, I appear to be one of their friends! I'm sure there's the makings of a security hole here... not to mention the way logging in produces an unexpected page! Also clicking on one of those friends (apart from me) produces another friend list - for someone else - which also includes me! shades of Zelig?