Our system automatically deletes
groups once they're empty (no
members). If you created the group,
you can delete the group by removing
all members and then yourself. Note
that if you were not the first admin
and creator of this group, you will
not be able to delete the group unless
the group creator has left it
voluntarily.
That's from Facebook Help, so my best suggestion is to make it open (or even closed, since one can ask to join a closed group) and let this take effect before your friend starts searching it. I could be wrong, but my guess is he could not find/join it because of the fact that the change is not instant.
Best Answer
The Facebook automatically enables "Group Insight" feature as soon as you have 250 members on your community.
For further information check out this post on Facebook's documentation.