I once posted what I thought was a light hearted response to a post. Only to find out that I had missed another post that made mine one of the most tastless disgusting comments ever.
I thankfully had people quickly update me on the situation and I was able to take down the post as soon as possible. Mistakes happen, I would give him the benefit of the doubt unless it becomes a recurring situation.
As to whether it's TMI, I guess it depends upon who she has as friends. If it truly is only a few close knit friends than I think it's appropriate, but if she is friends with over 50 people, I would think it was too much.