First question is why were you on your friend's computer? Was it in a place that was likely to be seen, thus could have been placed there for you to find, or do you think it wasn't meant to be found now before something has happened or found only if something happened?

And YES I would be concerned. I would talk to your friend, let them know that you are there to talk to them about anything and your friendship is unconditional.

There is such a stigma to mental illness many people are afraid to seek help they know they need.